auth.c

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/*-------------------------------------------------------------------------
 *
 * auth.c
 *    Routines to handle network authentication
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/libpq/auth.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <sys/param.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif

#include "commands/user.h"
#include "common/ip.h"
#include "common/md5.h"
#include "common/scram-common.h"
#include "libpq/auth.h"
#include "libpq/crypt.h"
#include "libpq/libpq.h"
#include "libpq/pqformat.h"
#include "libpq/scram.h"
#include "miscadmin.h"
#include "port/pg_bswap.h"
#include "replication/walsender.h"
#include "storage/ipc.h"
#include "utils/memutils.h"
#include "utils/timestamp.h"

/*----------------------------------------------------------------
 * Global authentication functions
 *----------------------------------------------------------------
 */
static void sendAuthRequest(Port *port, AuthRequest areq, const char *extradata,
                            int extralen);
static void auth_failed(Port *port, int status, char *logdetail);
static char *recv_password_packet(Port *port);


/*----------------------------------------------------------------
 * Password-based authentication methods (password, md5, and scram-sha-256)
 *----------------------------------------------------------------
 */
static int  CheckPasswordAuth(Port *port, char **logdetail);
static int  CheckPWChallengeAuth(Port *port, char **logdetail);

static int  CheckMD5Auth(Port *port, char *shadow_pass, char **logdetail);
static int  CheckSCRAMAuth(Port *port, char *shadow_pass, char **logdetail);


/*----------------------------------------------------------------
 * Ident authentication
 *----------------------------------------------------------------
 */
/* Max size of username ident server can return (per RFC 1413) */
#define IDENT_USERNAME_MAX 512

/* Standard TCP port number for Ident service.  Assigned by IANA */
#define IDENT_PORT 113

static int  ident_inet(hbaPort *port);


/*----------------------------------------------------------------
 * Peer authentication
 *----------------------------------------------------------------
 */
static int  auth_peer(hbaPort *port);


/*----------------------------------------------------------------
 * PAM authentication
 *----------------------------------------------------------------
 */
#ifdef USE_PAM
#ifdef HAVE_PAM_PAM_APPL_H
#include <pam/pam_appl.h>
#endif
#ifdef HAVE_SECURITY_PAM_APPL_H
#include <security/pam_appl.h>
#endif

#define PGSQL_PAM_SERVICE "postgresql"  /* Service name passed to PAM */

static int  CheckPAMAuth(Port *port, const char *user, const char *password);
static int  pam_passwd_conv_proc(int num_msg, const struct pam_message **msg,
                                 struct pam_response **resp, void *appdata_ptr);

static struct pam_conv pam_passw_conv = {
    &pam_passwd_conv_proc,
    NULL
};

static const char *pam_passwd = NULL;   /* Workaround for Solaris 2.6
                                         * brokenness */
static Port *pam_port_cludge;   /* Workaround for passing "Port *port" into
                                 * pam_passwd_conv_proc */
static bool pam_no_password;    /* For detecting no-password-given */
#endif                          /* USE_PAM */


/*----------------------------------------------------------------
 * BSD authentication
 *----------------------------------------------------------------
 */
#ifdef USE_BSD_AUTH
#include <bsd_auth.h>

static int  CheckBSDAuth(Port *port, char *user);
#endif                          /* USE_BSD_AUTH */


/*----------------------------------------------------------------
 * LDAP authentication
 *----------------------------------------------------------------
 */
#ifdef USE_LDAP
#ifndef WIN32
/* We use a deprecated function to keep the codepath the same as win32. */
#define LDAP_DEPRECATED 1
#include <ldap.h>
#else
#include <winldap.h>

/* Correct header from the Platform SDK */
typedef
ULONG       (*__ldap_start_tls_sA) (IN PLDAP ExternalHandle,
                                    OUT PULONG ServerReturnValue,
                                    OUT LDAPMessage **result,
                                    IN PLDAPControlA * ServerControls,
                                    IN PLDAPControlA * ClientControls
);
#endif

static int  CheckLDAPAuth(Port *port);

/* LDAP_OPT_DIAGNOSTIC_MESSAGE is the newer spelling */
#ifndef LDAP_OPT_DIAGNOSTIC_MESSAGE
#define LDAP_OPT_DIAGNOSTIC_MESSAGE LDAP_OPT_ERROR_STRING
#endif

#endif                          /* USE_LDAP */

/*----------------------------------------------------------------
 * Cert authentication
 *----------------------------------------------------------------
 */
#ifdef USE_SSL
static int  CheckCertAuth(Port *port);
#endif


/*----------------------------------------------------------------
 * Kerberos and GSSAPI GUCs
 *----------------------------------------------------------------
 */
char       *pg_krb_server_keyfile;
bool        pg_krb_caseins_users;


/*----------------------------------------------------------------
 * GSSAPI Authentication
 *----------------------------------------------------------------
 */
#ifdef ENABLE_GSS
#include "libpq/be-gssapi-common.h"

static int  pg_GSS_checkauth(Port *port);
static int  pg_GSS_recvauth(Port *port);
#endif                          /* ENABLE_GSS */


/*----------------------------------------------------------------
 * SSPI Authentication
 *----------------------------------------------------------------
 */
#ifdef ENABLE_SSPI
typedef SECURITY_STATUS
            (WINAPI * QUERY_SECURITY_CONTEXT_TOKEN_FN) (PCtxtHandle, void **);
static int  pg_SSPI_recvauth(Port *port);
static int  pg_SSPI_make_upn(char *accountname,
                             size_t accountnamesize,
                             char *domainname,
                             size_t domainnamesize,
                             bool update_accountname);
#endif

/*----------------------------------------------------------------
 * RADIUS Authentication
 *----------------------------------------------------------------
 */
static int  CheckRADIUSAuth(Port *port);
static int  PerformRadiusTransaction(const char *server, const char *secret, const char *portstr, const char *identifier, const char *user_name, const char *passwd);


/*
 * Maximum accepted size of GSS and SSPI authentication tokens.
 *
 * Kerberos tickets are usually quite small, but the TGTs issued by Windows
 * domain controllers include an authorization field known as the Privilege
 * Attribute Certificate (PAC), which contains the user's Windows permissions
 * (group memberships etc.). The PAC is copied into all tickets obtained on
 * the basis of this TGT (even those issued by Unix realms which the Windows
 * realm trusts), and can be several kB in size. The maximum token size
 * accepted by Windows systems is determined by the MaxAuthToken Windows
 * registry setting. Microsoft recommends that it is not set higher than
 * 65535 bytes, so that seems like a reasonable limit for us as well.
 */
#define PG_MAX_AUTH_TOKEN_LENGTH    65535

/*
 * Maximum accepted size of SASL messages.
 *
 * The messages that the server or libpq generate are much smaller than this,
 * but have some headroom.
 */
#define PG_MAX_SASL_MESSAGE_LENGTH  1024

/*----------------------------------------------------------------
 * Global authentication functions
 *----------------------------------------------------------------
 */

/*
 * This hook allows plugins to get control following client authentication,
 * but before the user has been informed about the results.  It could be used
 * to record login events, insert a delay after failed authentication, etc.
 */
ClientAuthentication_hook_type ClientAuthentication_hook = NULL;

/*
 * Tell the user the authentication failed, but not (much about) why.
 *
 * There is a tradeoff here between security concerns and making life
 * unnecessarily difficult for legitimate users.  We would not, for example,
 * want to report the password we were expecting to receive...
 * But it seems useful to report the username and authorization method
 * in use, and these are items that must be presumed known to an attacker
 * anyway.
 * Note that many sorts of failure report additional information in the
 * postmaster log, which we hope is only readable by good guys.  In
 * particular, if logdetail isn't NULL, we send that string to the log.
 */
static void
auth_failed(Port *port, int status, char *logdetail)
{
    const char *errstr;
    char       *cdetail;
    int         errcode_return = ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION;

    /*
     * If we failed due to EOF from client, just quit; there's no point in
     * trying to send a message to the client, and not much point in logging
     * the failure in the postmaster log.  (Logging the failure might be
     * desirable, were it not for the fact that libpq closes the connection
     * unceremoniously if challenged for a password when it hasn't got one to
     * send.  We'll get a useless log entry for every psql connection under
     * password auth, even if it's perfectly successful, if we log STATUS_EOF
     * events.)
     */
    if (status == STATUS_EOF)
        proc_exit(0);

    switch (port->hba->auth_method)
    {
        case uaReject:
        case uaImplicitReject:
            errstr = gettext_noop("authentication failed for user \"%s\": host rejected");
            break;
        case uaTrust:
            errstr = gettext_noop("\"trust\" authentication failed for user \"%s\"");
            break;
        case uaIdent:
            errstr = gettext_noop("Ident authentication failed for user \"%s\"");
            break;
        case uaPeer:
            errstr = gettext_noop("Peer authentication failed for user \"%s\"");
            break;
        case uaPassword:
        case uaMD5:
        case uaSCRAM:
            errstr = gettext_noop("password authentication failed for user \"%s\"");
            /* We use it to indicate if a .pgpass password failed. */
            errcode_return = ERRCODE_INVALID_PASSWORD;
            break;
        case uaGSS:
            errstr = gettext_noop("GSSAPI authentication failed for user \"%s\"");
            break;
        case uaSSPI:
            errstr = gettext_noop("SSPI authentication failed for user \"%s\"");
            break;
        case uaPAM:
            errstr = gettext_noop("PAM authentication failed for user \"%s\"");
            break;
        case uaBSD:
            errstr = gettext_noop("BSD authentication failed for user \"%s\"");
            break;
        case uaLDAP:
            errstr = gettext_noop("LDAP authentication failed for user \"%s\"");
            break;
        case uaCert:
            errstr = gettext_noop("certificate authentication failed for user \"%s\"");
            break;
        case uaRADIUS:
            errstr = gettext_noop("RADIUS authentication failed for user \"%s\"");
            break;
        default:
            errstr = gettext_noop("authentication failed for user \"%s\": invalid authentication method");
            break;
    }

    cdetail = psprintf(_("Connection matched pg_hba.conf line %d: \"%s\""),
                       port->hba->linenumber, port->hba->rawline);
    if (logdetail)
        logdetail = psprintf("%s\n%s", logdetail, cdetail);
    else
        logdetail = cdetail;

    ereport(FATAL,
            (errcode(errcode_return),
             errmsg(errstr, port->user_name),
             logdetail ? errdetail_log("%s", logdetail) : 0));

    /* doesn't return */
}


/*
 * Client authentication starts here.  If there is an error, this
 * function does not return and the backend process is terminated.
 */
void
ClientAuthentication(Port *port)
{
    int         status = STATUS_ERROR;
    char       *logdetail = NULL;

    /*
     * Get the authentication method to use for this frontend/database
     * combination.  Note: we do not parse the file at this point; this has
     * already been done elsewhere.  hba.c dropped an error message into the
     * server logfile if parsing the hba config file failed.
     */
    hba_getauthmethod(port);

    CHECK_FOR_INTERRUPTS();

    /*
     * This is the first point where we have access to the hba record for the
     * current connection, so perform any verifications based on the hba
     * options field that should be done *before* the authentication here.
     */
    if (port->hba->clientcert != clientCertOff)
    {
        /* If we haven't loaded a root certificate store, fail */
        if (!secure_loaded_verify_locations())
            ereport(FATAL,
                    (errcode(ERRCODE_CONFIG_FILE_ERROR),
                     errmsg("client certificates can only be checked if a root certificate store is available")));

        /*
         * If we loaded a root certificate store, and if a certificate is
         * present on the client, then it has been verified against our root
         * certificate store, and the connection would have been aborted
         * already if it didn't verify ok.
         */
        if (!port->peer_cert_valid)
            ereport(FATAL,
                    (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
                     errmsg("connection requires a valid client certificate")));
    }

    /*
     * Now proceed to do the actual authentication check
     */
    switch (port->hba->auth_method)
    {
        case uaReject:

            /*
             * An explicit "reject" entry in pg_hba.conf.  This report exposes
             * the fact that there's an explicit reject entry, which is
             * perhaps not so desirable from a security standpoint; but the
             * message for an implicit reject could confuse the DBA a lot when
             * the true situation is a match to an explicit reject.  And we
             * don't want to change the message for an implicit reject.  As
             * noted below, the additional information shown here doesn't
             * expose anything not known to an attacker.
             */
            {
                char        hostinfo[NI_MAXHOST];
                const char *encryption_state;

                pg_getnameinfo_all(&port->raddr.addr, port->raddr.salen,
                                   hostinfo, sizeof(hostinfo),
                                   NULL, 0,
                                   NI_NUMERICHOST);

                encryption_state =
#ifdef ENABLE_GSS
                    (port->gss && port->gss->enc) ? _("GSS encryption") :
#endif
#ifdef USE_SSL
                    port->ssl_in_use ? _("SSL encryption") :
#endif
                    _("no encryption");

                if (am_walsender)
                    ereport(FATAL,
                            (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
                    /* translator: last %s describes encryption state */
                             errmsg("pg_hba.conf rejects replication connection for host \"%s\", user \"%s\", %s",
                                    hostinfo, port->user_name,
                                    encryption_state)));
                else
                    ereport(FATAL,
                            (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
                    /* translator: last %s describes encryption state */
                             errmsg("pg_hba.conf rejects connection for host \"%s\", user \"%s\", database \"%s\", %s",
                                    hostinfo, port->user_name,
                                    port->database_name,
                                    encryption_state)));
                break;
            }

        case uaImplicitReject:

            /*
             * No matching entry, so tell the user we fell through.
             *
             * NOTE: the extra info reported here is not a security breach,
             * because all that info is known at the frontend and must be
             * assumed known to bad guys.  We're merely helping out the less
             * clueful good guys.
             */
            {
                char        hostinfo[NI_MAXHOST];
                const char *encryption_state;

                pg_getnameinfo_all(&port->raddr.addr, port->raddr.salen,
                                   hostinfo, sizeof(hostinfo),
                                   NULL, 0,
                                   NI_NUMERICHOST);

                encryption_state =
#ifdef ENABLE_GSS
                    (port->gss && port->gss->enc) ? _("GSS encryption") :
#endif
#ifdef USE_SSL
                    port->ssl_in_use ? _("SSL encryption") :
#endif
                    _("no encryption");

#define HOSTNAME_LOOKUP_DETAIL(port) \
                (port->remote_hostname ? \
                 (port->remote_hostname_resolv == +1 ? \
                  errdetail_log("Client IP address resolved to \"%s\", forward lookup matches.", \
                                port->remote_hostname) : \
                  port->remote_hostname_resolv == 0 ? \
                  errdetail_log("Client IP address resolved to \"%s\", forward lookup not checked.", \
                                port->remote_hostname) : \
                  port->remote_hostname_resolv == -1 ? \
                  errdetail_log("Client IP address resolved to \"%s\", forward lookup does not match.", \
                                port->remote_hostname) : \
                  port->remote_hostname_resolv == -2 ? \
                  errdetail_log("Could not translate client host name \"%s\" to IP address: %s.", \
                                port->remote_hostname, \
                                gai_strerror(port->remote_hostname_errcode)) : \
                  0) \
                 : (port->remote_hostname_resolv == -2 ? \
                    errdetail_log("Could not resolve client IP address to a host name: %s.", \
                                  gai_strerror(port->remote_hostname_errcode)) : \
                    0))

                if (am_walsender)
                    ereport(FATAL,
                            (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
                    /* translator: last %s describes encryption state */
                             errmsg("no pg_hba.conf entry for replication connection from host \"%s\", user \"%s\", %s",
                                    hostinfo, port->user_name,
                                    encryption_state),
                             HOSTNAME_LOOKUP_DETAIL(port)));
                else
                    ereport(FATAL,
                            (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
                    /* translator: last %s describes encryption state */
                             errmsg("no pg_hba.conf entry for host \"%s\", user \"%s\", database \"%s\", %s",
                                    hostinfo, port->user_name,
                                    port->database_name,
                                    encryption_state),
                             HOSTNAME_LOOKUP_DETAIL(port)));
                break;
            }

        case uaGSS:
#ifdef ENABLE_GSS
            /* We might or might not have the gss workspace already */
            if (port->gss == NULL)
                port->gss = (pg_gssinfo *)
                    MemoryContextAllocZero(TopMemoryContext,
                                           sizeof(pg_gssinfo));
            port->gss->auth = true;

            /*
             * If GSS state was set up while enabling encryption, we can just
             * check the client's principal.  Otherwise, ask for it.
             */
            if (port->gss->enc)
                status = pg_GSS_checkauth(port);
            else
            {
                sendAuthRequest(port, AUTH_REQ_GSS, NULL, 0);
                status = pg_GSS_recvauth(port);
            }
#else
            Assert(false);
#endif
            break;

        case uaSSPI:
#ifdef ENABLE_SSPI
            if (port->gss == NULL)
                port->gss = (pg_gssinfo *)
                    MemoryContextAllocZero(TopMemoryContext,
                                           sizeof(pg_gssinfo));
            sendAuthRequest(port, AUTH_REQ_SSPI, NULL, 0);
            status = pg_SSPI_recvauth(port);
#else
            Assert(false);
#endif
            break;

        case uaPeer:
            status = auth_peer(port);
            break;

        case uaIdent:
            status = ident_inet(port);
            break;

        case uaMD5:
        case uaSCRAM:
            status = CheckPWChallengeAuth(port, &logdetail);
            break;

        case uaPassword:
            status = CheckPasswordAuth(port, &logdetail);
            break;

        case uaPAM:
#ifdef USE_PAM
            status = CheckPAMAuth(port, port->user_name, "");
#else
            Assert(false);
#endif                          /* USE_PAM */
            break;

        case uaBSD:
#ifdef USE_BSD_AUTH
            status = CheckBSDAuth(port, port->user_name);
#else
            Assert(false);
#endif                          /* USE_BSD_AUTH */
            break;

        case uaLDAP:
#ifdef USE_LDAP
            status = CheckLDAPAuth(port);
#else
            Assert(false);
#endif
            break;
        case uaRADIUS:
            status = CheckRADIUSAuth(port);
            break;
        case uaCert:
            /* uaCert will be treated as if clientcert=verify-full (uaTrust) */
        case uaTrust:
            status = STATUS_OK;
            break;
    }

    if ((status == STATUS_OK && port->hba->clientcert == clientCertFull)
        || port->hba->auth_method == uaCert)
    {
        /*
         * Make sure we only check the certificate if we use the cert method
         * or verify-full option.
         */
#ifdef USE_SSL
        status = CheckCertAuth(port);
#else
        Assert(false);
#endif
    }

    if (ClientAuthentication_hook)
        (*ClientAuthentication_hook) (port, status);

    if (status == STATUS_OK)
        sendAuthRequest(port, AUTH_REQ_OK, NULL, 0);
    else
        auth_failed(port, status, logdetail);
}


/*
 * Send an authentication request packet to the frontend.
 */
static void
sendAuthRequest(Port *port, AuthRequest areq, const char *extradata, int extralen)
{
    StringInfoData buf;

    CHECK_FOR_INTERRUPTS();

    pq_beginmessage(&buf, 'R');
    pq_sendint32(&buf, (int32) areq);
    if (extralen > 0)
        pq_sendbytes(&buf, extradata, extralen);

    pq_endmessage(&buf);

    /*
     * Flush message so client will see it, except for AUTH_REQ_OK and
     * AUTH_REQ_SASL_FIN, which need not be sent until we are ready for
     * queries.
     */
    if (areq != AUTH_REQ_OK && areq != AUTH_REQ_SASL_FIN)
        pq_flush();

    CHECK_FOR_INTERRUPTS();
}

/*
 * Collect password response packet from frontend.
 *
 * Returns NULL if couldn't get password, else palloc'd string.
 */
static char *
recv_password_packet(Port *port)
{
    StringInfoData buf;

    pq_startmsgread();
    if (PG_PROTOCOL_MAJOR(port->proto) >= 3)
    {
        /* Expect 'p' message type */
        int         mtype;

        mtype = pq_getbyte();
        if (mtype != 'p')
        {
            /*
             * If the client just disconnects without offering a password,
             * don't make a log entry.  This is legal per protocol spec and in
             * fact commonly done by psql, so complaining just clutters the
             * log.
             */
            if (mtype != EOF)
                ereport(ERROR,
                        (errcode(ERRCODE_PROTOCOL_VIOLATION),
                         errmsg("expected password response, got message type %d",
                                mtype)));
            return NULL;        /* EOF or bad message type */
        }
    }
    else
    {
        /* For pre-3.0 clients, avoid log entry if they just disconnect */
        if (pq_peekbyte() == EOF)
            return NULL;        /* EOF */
    }

    initStringInfo(&buf);
    if (pq_getmessage(&buf, 0)) /* receive password */
    {
        /* EOF - pq_getmessage already logged a suitable message */
        pfree(buf.data);
        return NULL;
    }

    /*
     * Apply sanity check: password packet length should agree with length of
     * contained string.  Note it is safe to use strlen here because
     * StringInfo is guaranteed to have an appended '\0'.
     */
    if (strlen(buf.data) + 1 != buf.len)
        ereport(ERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg("invalid password packet size")));

    /*
     * Don't allow an empty password. Libpq treats an empty password the same
     * as no password at all, and won't even try to authenticate. But other
     * clients might, so allowing it would be confusing.
     *
     * Note that this only catches an empty password sent by the client in
     * plaintext. There's also a check in CREATE/ALTER USER that prevents an
     * empty string from being stored as a user's password in the first place.
     * We rely on that for MD5 and SCRAM authentication, but we still need
     * this check here, to prevent an empty password from being used with
     * authentication methods that check the password against an external
     * system, like PAM, LDAP and RADIUS.
     */
    if (buf.len == 1)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PASSWORD),
                 errmsg("empty password returned by client")));

    /* Do not echo password to logs, for security. */
    elog(DEBUG5, "received password packet");

    /*
     * Return the received string.  Note we do not attempt to do any
     * character-set conversion on it; since we don't yet know the client's
     * encoding, there wouldn't be much point.
     */
    return buf.data;
}


/*----------------------------------------------------------------
 * Password-based authentication mechanisms
 *----------------------------------------------------------------
 */

/*
 * Plaintext password authentication.
 */
static int
CheckPasswordAuth(Port *port, char **logdetail)
{
    char       *passwd;
    int         result;
    char       *shadow_pass;

    sendAuthRequest(port, AUTH_REQ_PASSWORD, NULL, 0);

    passwd = recv_password_packet(port);
    if (passwd == NULL)
        return STATUS_EOF;      /* client wouldn't send password */

    shadow_pass = get_role_password(port->user_name, logdetail);
    if (shadow_pass)
    {
        result = plain_crypt_verify(port->user_name, shadow_pass, passwd,
                                    logdetail);
    }
    else
        result = STATUS_ERROR;

    if (shadow_pass)
        pfree(shadow_pass);
    pfree(passwd);

    return result;
}

/*
 * MD5 and SCRAM authentication.
 */
static int
CheckPWChallengeAuth(Port *port, char **logdetail)
{
    int         auth_result;
    char       *shadow_pass;
    PasswordType pwtype;

    Assert(port->hba->auth_method == uaSCRAM ||
           port->hba->auth_method == uaMD5);

    /* First look up the user's password. */
    shadow_pass = get_role_password(port->user_name, logdetail);

    /*
     * If the user does not exist, or has no password or it's expired, we
     * still go through the motions of authentication, to avoid revealing to
     * the client that the user didn't exist.  If 'md5' is allowed, we choose
     * whether to use 'md5' or 'scram-sha-256' authentication based on current
     * password_encryption setting.  The idea is that most genuine users
     * probably have a password of that type, and if we pretend that this user
     * had a password of that type, too, it "blends in" best.
     */
    if (!shadow_pass)
        pwtype = Password_encryption;
    else
        pwtype = get_password_type(shadow_pass);

    /*
     * If 'md5' authentication is allowed, decide whether to perform 'md5' or
     * 'scram-sha-256' authentication based on the type of password the user
     * has.  If it's an MD5 hash, we must do MD5 authentication, and if it's a
     * SCRAM secret, we must do SCRAM authentication.
     *
     * If MD5 authentication is not allowed, always use SCRAM.  If the user
     * had an MD5 password, CheckSCRAMAuth() will fail.
     */
    if (port->hba->auth_method == uaMD5 && pwtype == PASSWORD_TYPE_MD5)
        auth_result = CheckMD5Auth(port, shadow_pass, logdetail);
    else
        auth_result = CheckSCRAMAuth(port, shadow_pass, logdetail);

    if (shadow_pass)
        pfree(shadow_pass);

    /*
     * If get_role_password() returned error, return error, even if the
     * authentication succeeded.
     */
    if (!shadow_pass)
    {
        Assert(auth_result != STATUS_OK);
        return STATUS_ERROR;
    }
    return auth_result;
}

static int
CheckMD5Auth(Port *port, char *shadow_pass, char **logdetail)
{
    char        md5Salt[4];     /* Password salt */
    char       *passwd;
    int         result;

    if (Db_user_namespace)
        ereport(FATAL,
                (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
                 errmsg("MD5 authentication is not supported when \"db_user_namespace\" is enabled")));

    /* include the salt to use for computing the response */
    if (!pg_strong_random(md5Salt, 4))
    {
        ereport(LOG,
                (errmsg("could not generate random MD5 salt")));
        return STATUS_ERROR;
    }

    sendAuthRequest(port, AUTH_REQ_MD5, md5Salt, 4);

    passwd = recv_password_packet(port);
    if (passwd == NULL)
        return STATUS_EOF;      /* client wouldn't send password */

    if (shadow_pass)
        result = md5_crypt_verify(port->user_name, shadow_pass, passwd,
                                  md5Salt, 4, logdetail);
    else
        result = STATUS_ERROR;

    pfree(passwd);

    return result;
}

static int
CheckSCRAMAuth(Port *port, char *shadow_pass, char **logdetail)
{
    StringInfoData sasl_mechs;
    int         mtype;
    StringInfoData buf;
    void       *scram_opaq = NULL;
    char       *output = NULL;
    int         outputlen = 0;
    const char *input;
    int         inputlen;
    int         result;
    bool        initial;

    /*
     * SASL auth is not supported for protocol versions before 3, because it
     * relies on the overall message length word to determine the SASL payload
     * size in AuthenticationSASLContinue and PasswordMessage messages.  (We
     * used to have a hard rule that protocol messages must be parsable
     * without relying on the length word, but we hardly care about older
     * protocol version anymore.)
     */
    if (PG_PROTOCOL_MAJOR(FrontendProtocol) < 3)
        ereport(FATAL,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("SASL authentication is not supported in protocol version 2")));

    /*
     * Send the SASL authentication request to user.  It includes the list of
     * authentication mechanisms that are supported.
     */
    initStringInfo(&sasl_mechs);

    pg_be_scram_get_mechanisms(port, &sasl_mechs);
    /* Put another '\0' to mark that list is finished. */
    appendStringInfoChar(&sasl_mechs, '\0');

    sendAuthRequest(port, AUTH_REQ_SASL, sasl_mechs.data, sasl_mechs.len);
    pfree(sasl_mechs.data);

    /*
     * Loop through SASL message exchange.  This exchange can consist of
     * multiple messages sent in both directions.  First message is always
     * from the client.  All messages from client to server are password
     * packets (type 'p').
     */
    initial = true;
    do
    {
        pq_startmsgread();
        mtype = pq_getbyte();
        if (mtype != 'p')
        {
            /* Only log error if client didn't disconnect. */
            if (mtype != EOF)
            {
                ereport(ERROR,
                        (errcode(ERRCODE_PROTOCOL_VIOLATION),
                         errmsg("expected SASL response, got message type %d",
                                mtype)));
            }
            else
                return STATUS_EOF;
        }

        /* Get the actual SASL message */
        initStringInfo(&buf);
        if (pq_getmessage(&buf, PG_MAX_SASL_MESSAGE_LENGTH))
        {
            /* EOF - pq_getmessage already logged error */
            pfree(buf.data);
            return STATUS_ERROR;
        }

        elog(DEBUG4, "processing received SASL response of length %d", buf.len);

        /*
         * The first SASLInitialResponse message is different from the others.
         * It indicates which SASL mechanism the client selected, and contains
         * an optional Initial Client Response payload.  The subsequent
         * SASLResponse messages contain just the SASL payload.
         */
        if (initial)
        {
            const char *selected_mech;

            selected_mech = pq_getmsgrawstring(&buf);

            /*
             * Initialize the status tracker for message exchanges.
             *
             * If the user doesn't exist, or doesn't have a valid password, or
             * it's expired, we still go through the motions of SASL
             * authentication, but tell the authentication method that the
             * authentication is "doomed". That is, it's going to fail, no
             * matter what.
             *
             * This is because we don't want to reveal to an attacker what
             * usernames are valid, nor which users have a valid password.
             */
            scram_opaq = pg_be_scram_init(port, selected_mech, shadow_pass);

            inputlen = pq_getmsgint(&buf, 4);
            if (inputlen == -1)
                input = NULL;
            else
                input = pq_getmsgbytes(&buf, inputlen);

            initial = false;
        }
        else
        {
            inputlen = buf.len;
            input = pq_getmsgbytes(&buf, buf.len);
        }
        pq_getmsgend(&buf);

        /*
         * The StringInfo guarantees that there's a \0 byte after the
         * response.
         */
        Assert(input == NULL || input[inputlen] == '\0');

        /*
         * we pass 'logdetail' as NULL when doing a mock authentication,
         * because we should already have a better error message in that case
         */
        result = pg_be_scram_exchange(scram_opaq, input, inputlen,
                                      &output, &outputlen,
                                      logdetail);

        /* input buffer no longer used */
        pfree(buf.data);

        if (output)
        {
            /*
             * Negotiation generated data to be sent to the client.
             */
            elog(DEBUG4, "sending SASL challenge of length %u", outputlen);

            if (result == SASL_EXCHANGE_SUCCESS)
                sendAuthRequest(port, AUTH_REQ_SASL_FIN, output, outputlen);
            else
                sendAuthRequest(port, AUTH_REQ_SASL_CONT, output, outputlen);

            pfree(output);
        }
    } while (result == SASL_EXCHANGE_CONTINUE);

    /* Oops, Something bad happened */
    if (result != SASL_EXCHANGE_SUCCESS)
    {
        return STATUS_ERROR;
    }

    return STATUS_OK;
}


/*----------------------------------------------------------------
 * GSSAPI authentication system
 *----------------------------------------------------------------
 */
#ifdef ENABLE_GSS
static int
pg_GSS_recvauth(Port *port)
{
    OM_uint32   maj_stat,
                min_stat,
                lmin_s,
                gflags;
    int         mtype;
    StringInfoData buf;
    gss_buffer_desc gbuf;

    /*
     * GSS auth is not supported for protocol versions before 3, because it
     * relies on the overall message length word to determine the GSS payload
     * size in AuthenticationGSSContinue and PasswordMessage messages. (This
     * is, in fact, a design error in our GSS support, because protocol
     * messages are supposed to be parsable without relying on the length
     * word; but it's not worth changing it now.)
     */
    if (PG_PROTOCOL_MAJOR(FrontendProtocol) < 3)
        ereport(FATAL,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("GSSAPI is not supported in protocol version 2")));

    /*
     * Use the configured keytab, if there is one.  Unfortunately, Heimdal
     * doesn't support the cred store extensions, so use the env var.
     */
    if (pg_krb_server_keyfile != NULL && pg_krb_server_keyfile[0] != '\0')
    {
        if (setenv("KRB5_KTNAME", pg_krb_server_keyfile, 1) != 0)
        {
            /* The only likely failure cause is OOM, so use that errcode */
            ereport(FATAL,
                    (errcode(ERRCODE_OUT_OF_MEMORY),
                     errmsg("could not set environment: %m")));
        }
    }

    /*
     * We accept any service principal that's present in our keytab. This
     * increases interoperability between kerberos implementations that see
     * for example case sensitivity differently, while not really opening up
     * any vector of attack.
     */
    port->gss->cred = GSS_C_NO_CREDENTIAL;

    /*
     * Initialize sequence with an empty context
     */
    port->gss->ctx = GSS_C_NO_CONTEXT;

    /*
     * Loop through GSSAPI message exchange. This exchange can consist of
     * multiple messages sent in both directions. First message is always from
     * the client. All messages from client to server are password packets
     * (type 'p').
     */
    do
    {
        pq_startmsgread();

        CHECK_FOR_INTERRUPTS();

        mtype = pq_getbyte();
        if (mtype != 'p')
        {
            /* Only log error if client didn't disconnect. */
            if (mtype != EOF)
                ereport(ERROR,
                        (errcode(ERRCODE_PROTOCOL_VIOLATION),
                         errmsg("expected GSS response, got message type %d",
                                mtype)));
            return STATUS_ERROR;
        }

        /* Get the actual GSS token */
        initStringInfo(&buf);
        if (pq_getmessage(&buf, PG_MAX_AUTH_TOKEN_LENGTH))
        {
            /* EOF - pq_getmessage already logged error */
            pfree(buf.data);
            return STATUS_ERROR;
        }

        /* Map to GSSAPI style buffer */
        gbuf.length = buf.len;
        gbuf.value = buf.data;

        elog(DEBUG4, "processing received GSS token of length %u",
             (unsigned int) gbuf.length);

        maj_stat = gss_accept_sec_context(&min_stat,
                                          &port->gss->ctx,
                                          port->gss->cred,
                                          &gbuf,
                                          GSS_C_NO_CHANNEL_BINDINGS,
                                          &port->gss->name,
                                          NULL,
                                          &port->gss->outbuf,
                                          &gflags,
                                          NULL,
                                          NULL);

        /* gbuf no longer used */
        pfree(buf.data);

        elog(DEBUG5, "gss_accept_sec_context major: %d, "
             "minor: %d, outlen: %u, outflags: %x",
             maj_stat, min_stat,
             (unsigned int) port->gss->outbuf.length, gflags);

        CHECK_FOR_INTERRUPTS();

        if (port->gss->outbuf.length != 0)
        {
            /*
             * Negotiation generated data to be sent to the client.
             */
            elog(DEBUG4, "sending GSS response token of length %u",
                 (unsigned int) port->gss->outbuf.length);

            sendAuthRequest(port, AUTH_REQ_GSS_CONT,
                            port->gss->outbuf.value, port->gss->outbuf.length);

            gss_release_buffer(&lmin_s, &port->gss->outbuf);
        }

        if (maj_stat != GSS_S_COMPLETE && maj_stat != GSS_S_CONTINUE_NEEDED)
        {
            gss_delete_sec_context(&lmin_s, &port->gss->ctx, GSS_C_NO_BUFFER);
            pg_GSS_error(_("accepting GSS security context failed"),
                         maj_stat, min_stat);
            return STATUS_ERROR;
        }

        if (maj_stat == GSS_S_CONTINUE_NEEDED)
            elog(DEBUG4, "GSS continue needed");

    } while (maj_stat == GSS_S_CONTINUE_NEEDED);

    if (port->gss->cred != GSS_C_NO_CREDENTIAL)
    {
        /*
         * Release service principal credentials
         */
        gss_release_cred(&min_stat, &port->gss->cred);
    }
    return pg_GSS_checkauth(port);
}

/*
 * Check whether the GSSAPI-authenticated user is allowed to connect as the
 * claimed username.
 */
static int
pg_GSS_checkauth(Port *port)
{
    int         ret;
    OM_uint32   maj_stat,
                min_stat,
                lmin_s;
    gss_buffer_desc gbuf;

    /*
     * Get the name of the user that authenticated, and compare it to the pg
     * username that was specified for the connection.
     */
    maj_stat = gss_display_name(&min_stat, port->gss->name, &gbuf, NULL);
    if (maj_stat != GSS_S_COMPLETE)
    {
        pg_GSS_error(_("retrieving GSS user name failed"),
                     maj_stat, min_stat);
        return STATUS_ERROR;
    }

    /*
     * Copy the original name of the authenticated principal into our backend
     * memory for display later.
     */
    port->gss->princ = MemoryContextStrdup(TopMemoryContext, gbuf.value);

    /*
     * Split the username at the realm separator
     */
    if (strchr(gbuf.value, '@'))
    {
        char       *cp = strchr(gbuf.value, '@');

        /*
         * If we are not going to include the realm in the username that is
         * passed to the ident map, destructively modify it here to remove the
         * realm. Then advance past the separator to check the realm.
         */
        if (!port->hba->include_realm)
            *cp = '\0';
        cp++;

        if (port->hba->krb_realm != NULL && strlen(port->hba->krb_realm))
        {
            /*
             * Match the realm part of the name first
             */
            if (pg_krb_caseins_users)
                ret = pg_strcasecmp(port->hba->krb_realm, cp);
            else
                ret = strcmp(port->hba->krb_realm, cp);

            if (ret)
            {
                /* GSS realm does not match */
                elog(DEBUG2,
                     "GSSAPI realm (%s) and configured realm (%s) don't match",
                     cp, port->hba->krb_realm);
                gss_release_buffer(&lmin_s, &gbuf);
                return STATUS_ERROR;
            }
        }
    }
    else if (port->hba->krb_realm && strlen(port->hba->krb_realm))
    {
        elog(DEBUG2,
             "GSSAPI did not return realm but realm matching was requested");

        gss_release_buffer(&lmin_s, &gbuf);
        return STATUS_ERROR;
    }

    ret = check_usermap(port->hba->usermap, port->user_name, gbuf.value,
                        pg_krb_caseins_users);

    gss_release_buffer(&lmin_s, &gbuf);

    return ret;
}
#endif                          /* ENABLE_GSS */


/*----------------------------------------------------------------
 * SSPI authentication system
 *----------------------------------------------------------------
 */
#ifdef ENABLE_SSPI

/*
 * Generate an error for SSPI authentication.  The caller should apply
 * _() to errmsg to make it translatable.
 */
static void
pg_SSPI_error(int severity, const char *errmsg, SECURITY_STATUS r)
{
    char        sysmsg[256];

    if (FormatMessage(FORMAT_MESSAGE_IGNORE_INSERTS |
                      FORMAT_MESSAGE_FROM_SYSTEM,
                      NULL, r, 0,
                      sysmsg, sizeof(sysmsg), NULL) == 0)
        ereport(severity,
                (errmsg_internal("%s", errmsg),
                 errdetail_internal("SSPI error %x", (unsigned int) r)));
    else
        ereport(severity,
                (errmsg_internal("%s", errmsg),
                 errdetail_internal("%s (%x)", sysmsg, (unsigned int) r)));
}

static int
pg_SSPI_recvauth(Port *port)
{
    int         mtype;
    StringInfoData buf;
    SECURITY_STATUS r;
    CredHandle  sspicred;
    CtxtHandle *sspictx = NULL,
                newctx;
    TimeStamp   expiry;
    ULONG       contextattr;
    SecBufferDesc inbuf;
    SecBufferDesc outbuf;
    SecBuffer   OutBuffers[1];
    SecBuffer   InBuffers[1];
    HANDLE      token;
    TOKEN_USER *tokenuser;
    DWORD       retlen;
    char        accountname[MAXPGPATH];
    char        domainname[MAXPGPATH];
    DWORD       accountnamesize = sizeof(accountname);
    DWORD       domainnamesize = sizeof(domainname);
    SID_NAME_USE accountnameuse;
    HMODULE     secur32;

    QUERY_SECURITY_CONTEXT_TOKEN_FN _QuerySecurityContextToken;

    /*
     * SSPI auth is not supported for protocol versions before 3, because it
     * relies on the overall message length word to determine the SSPI payload
     * size in AuthenticationGSSContinue and PasswordMessage messages. (This
     * is, in fact, a design error in our SSPI support, because protocol
     * messages are supposed to be parsable without relying on the length
     * word; but it's not worth changing it now.)
     */
    if (PG_PROTOCOL_MAJOR(FrontendProtocol) < 3)
        ereport(FATAL,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("SSPI is not supported in protocol version 2")));

    /*
     * Acquire a handle to the server credentials.
     */
    r = AcquireCredentialsHandle(NULL,
                                 "negotiate",
                                 SECPKG_CRED_INBOUND,
                                 NULL,
                                 NULL,
                                 NULL,
                                 NULL,
                                 &sspicred,
                                 &expiry);
    if (r != SEC_E_OK)
        pg_SSPI_error(ERROR, _("could not acquire SSPI credentials"), r);

    /*
     * Loop through SSPI message exchange. This exchange can consist of
     * multiple messages sent in both directions. First message is always from
     * the client. All messages from client to server are password packets
     * (type 'p').
     */
    do
    {
        pq_startmsgread();
        mtype = pq_getbyte();
        if (mtype != 'p')
        {
            if (sspictx != NULL)
            {
                DeleteSecurityContext(sspictx);
                free(sspictx);
            }
            FreeCredentialsHandle(&sspicred);

            /* Only log error if client didn't disconnect. */
            if (mtype != EOF)
                ereport(ERROR,
                        (errcode(ERRCODE_PROTOCOL_VIOLATION),
                         errmsg("expected SSPI response, got message type %d",
                                mtype)));
            return STATUS_ERROR;
        }

        /* Get the actual SSPI token */
        initStringInfo(&buf);
        if (pq_getmessage(&buf, PG_MAX_AUTH_TOKEN_LENGTH))
        {
            /* EOF - pq_getmessage already logged error */
            pfree(buf.data);
            if (sspictx != NULL)
            {
                DeleteSecurityContext(sspictx);
                free(sspictx);
            }
            FreeCredentialsHandle(&sspicred);
            return STATUS_ERROR;
        }

        /* Map to SSPI style buffer */
        inbuf.ulVersion = SECBUFFER_VERSION;
        inbuf.cBuffers = 1;
        inbuf.pBuffers = InBuffers;
        InBuffers[0].pvBuffer = buf.data;
        InBuffers[0].cbBuffer = buf.len;
        InBuffers[0].BufferType = SECBUFFER_TOKEN;

        /* Prepare output buffer */
        OutBuffers[0].pvBuffer = NULL;
        OutBuffers[0].BufferType = SECBUFFER_TOKEN;
        OutBuffers[0].cbBuffer = 0;
        outbuf.cBuffers = 1;
        outbuf.pBuffers = OutBuffers;
        outbuf.ulVersion = SECBUFFER_VERSION;

        elog(DEBUG4, "processing received SSPI token of length %u",
             (unsigned int) buf.len);

        r = AcceptSecurityContext(&sspicred,
                                  sspictx,
                                  &inbuf,
                                  ASC_REQ_ALLOCATE_MEMORY,
                                  SECURITY_NETWORK_DREP,
                                  &newctx,
                                  &outbuf,
                                  &contextattr,
                                  NULL);

        /* input buffer no longer used */
        pfree(buf.data);

        if (outbuf.cBuffers > 0 && outbuf.pBuffers[0].cbBuffer > 0)
        {
            /*
             * Negotiation generated data to be sent to the client.
             */
            elog(DEBUG4, "sending SSPI response token of length %u",
                 (unsigned int) outbuf.pBuffers[0].cbBuffer);

            port->gss->outbuf.length = outbuf.pBuffers[0].cbBuffer;
            port->gss->outbuf.value = outbuf.pBuffers[0].pvBuffer;

            sendAuthRequest(port, AUTH_REQ_GSS_CONT,
                            port->gss->outbuf.value, port->gss->outbuf.length);

            FreeContextBuffer(outbuf.pBuffers[0].pvBuffer);
        }

        if (r != SEC_E_OK && r != SEC_I_CONTINUE_NEEDED)
        {
            if (sspictx != NULL)
            {
                DeleteSecurityContext(sspictx);
                free(sspictx);
            }
            FreeCredentialsHandle(&sspicred);
            pg_SSPI_error(ERROR,
                          _("could not accept SSPI security context"), r);
        }

        /*
         * Overwrite the current context with the one we just received. If
         * sspictx is NULL it was the first loop and we need to allocate a
         * buffer for it. On subsequent runs, we can just overwrite the buffer
         * contents since the size does not change.
         */
        if (sspictx == NULL)
        {
            sspictx = malloc(sizeof(CtxtHandle));
            if (sspictx == NULL)
                ereport(ERROR,
                        (errmsg("out of memory")));
        }

        memcpy(sspictx, &newctx, sizeof(CtxtHandle));

        if (r == SEC_I_CONTINUE_NEEDED)
            elog(DEBUG4, "SSPI continue needed");

    } while (r == SEC_I_CONTINUE_NEEDED);


    /*
     * Release service principal credentials
     */
    FreeCredentialsHandle(&sspicred);


    /*
     * SEC_E_OK indicates that authentication is now complete.
     *
     * Get the name of the user that authenticated, and compare it to the pg
     * username that was specified for the connection.
     *
     * MingW is missing the export for QuerySecurityContextToken in the
     * secur32 library, so we have to load it dynamically.
     */

    secur32 = LoadLibrary("SECUR32.DLL");
    if (secur32 == NULL)
        ereport(ERROR,
                (errmsg("could not load library \"%s\": error code %lu",
                        "SECUR32.DLL", GetLastError())));

    _QuerySecurityContextToken = (QUERY_SECURITY_CONTEXT_TOKEN_FN) (pg_funcptr_t)
        GetProcAddress(secur32, "QuerySecurityContextToken");
    if (_QuerySecurityContextToken == NULL)
    {
        FreeLibrary(secur32);
        ereport(ERROR,
                (errmsg_internal("could not locate QuerySecurityContextToken in secur32.dll: error code %lu",
                                 GetLastError())));
    }

    r = (_QuerySecurityContextToken) (sspictx, &token);
    if (r != SEC_E_OK)
    {
        FreeLibrary(secur32);
        pg_SSPI_error(ERROR,
                      _("could not get token from SSPI security context"), r);
    }

    FreeLibrary(secur32);

    /*
     * No longer need the security context, everything from here on uses the
     * token instead.
     */
    DeleteSecurityContext(sspictx);
    free(sspictx);

    if (!GetTokenInformation(token, TokenUser, NULL, 0, &retlen) && GetLastError() != 122)
        ereport(ERROR,
                (errmsg_internal("could not get token information buffer size: error code %lu",
                                 GetLastError())));

    tokenuser = malloc(retlen);
    if (tokenuser == NULL)
        ereport(ERROR,
                (errmsg("out of memory")));

    if (!GetTokenInformation(token, TokenUser, tokenuser, retlen, &retlen))
        ereport(ERROR,
                (errmsg_internal("could not get token information: error code %lu",
                                 GetLastError())));

    CloseHandle(token);

    if (!LookupAccountSid(NULL, tokenuser->User.Sid, accountname, &accountnamesize,
                          domainname, &domainnamesize, &accountnameuse))
        ereport(ERROR,
                (errmsg_internal("could not look up account SID: error code %lu",
                                 GetLastError())));

    free(tokenuser);

    if (!port->hba->compat_realm)
    {
        int         status = pg_SSPI_make_upn(accountname, sizeof(accountname),
                                              domainname, sizeof(domainname),
                                              port->hba->upn_username);

        if (status != STATUS_OK)
            /* Error already reported from pg_SSPI_make_upn */
            return status;
    }

    /*
     * Compare realm/domain if requested. In SSPI, always compare case
     * insensitive.
     */
    if (port->hba->krb_realm && strlen(port->hba->krb_realm))
    {
        if (pg_strcasecmp(port->hba->krb_realm, domainname) != 0)
        {
            elog(DEBUG2,
                 "SSPI domain (%s) and configured domain (%s) don't match",
                 domainname, port->hba->krb_realm);

            return STATUS_ERROR;
        }
    }

    /*
     * We have the username (without domain/realm) in accountname, compare to
     * the supplied value. In SSPI, always compare case insensitive.
     *
     * If set to include realm, append it in <username>@<realm> format.
     */
    if (port->hba->include_realm)
    {
        char       *namebuf;
        int         retval;

        namebuf = psprintf("%s@%s", accountname, domainname);
        retval = check_usermap(port->hba->usermap, port->user_name, namebuf, true);
        pfree(namebuf);
        return retval;
    }
    else
        return check_usermap(port->hba->usermap, port->user_name, accountname, true);
}

/*
 * Replaces the domainname with the Kerberos realm name,
 * and optionally the accountname with the Kerberos user name.
 */
static int
pg_SSPI_make_upn(char *accountname,
                 size_t accountnamesize,
                 char *domainname,
                 size_t domainnamesize,
                 bool update_accountname)
{
    char       *samname;
    char       *upname = NULL;
    char       *p = NULL;
    ULONG       upnamesize = 0;
    size_t      upnamerealmsize;
    BOOLEAN     res;

    /*
     * Build SAM name (DOMAIN\user), then translate to UPN
     * (user@kerberos.realm). The realm name is returned in lower case, but
     * that is fine because in SSPI auth, string comparisons are always
     * case-insensitive.
     */

    samname = psprintf("%s\\%s", domainname, accountname);
    res = TranslateName(samname, NameSamCompatible, NameUserPrincipal,
                        NULL, &upnamesize);

    if ((!res && GetLastError() != ERROR_INSUFFICIENT_BUFFER)
        || upnamesize == 0)
    {
        pfree(samname);
        ereport(LOG,
                (errcode(ERRCODE_INVALID_ROLE_SPECIFICATION),
                 errmsg("could not translate name")));
        return STATUS_ERROR;
    }

    /* upnamesize includes the terminating NUL. */
    upname = palloc(upnamesize);

    res = TranslateName(samname, NameSamCompatible, NameUserPrincipal,
                        upname, &upnamesize);

    pfree(samname);
    if (res)
        p = strchr(upname, '@');

    if (!res || p == NULL)
    {
        pfree(upname);
        ereport(LOG,
                (errcode(ERRCODE_INVALID_ROLE_SPECIFICATION),
                 errmsg("could not translate name")));
        return STATUS_ERROR;
    }

    /* Length of realm name after the '@', including the NUL. */
    upnamerealmsize = upnamesize - (p - upname + 1);

    /* Replace domainname with realm name. */
    if (upnamerealmsize > domainnamesize)
    {
        pfree(upname);
        ereport(LOG,
                (errcode(ERRCODE_INVALID_ROLE_SPECIFICATION),
                 errmsg("realm name too long")));
        return STATUS_ERROR;
    }

    /* Length is now safe. */
    strcpy(domainname, p + 1);

    /* Replace account name as well (in case UPN != SAM)? */
    if (update_accountname)
    {
        if ((p - upname + 1) > accountnamesize)
        {
            pfree(upname);
            ereport(LOG,
                    (errcode(ERRCODE_INVALID_ROLE_SPECIFICATION),
                     errmsg("translated account name too long")));
            return STATUS_ERROR;
        }

        *p = 0;
        strcpy(accountname, upname);
    }

    pfree(upname);
    return STATUS_OK;
}
#endif                          /* ENABLE_SSPI */



/*----------------------------------------------------------------
 * Ident authentication system
 *----------------------------------------------------------------
 */

/*
 *  Parse the string "*ident_response" as a response from a query to an Ident
 *  server.  If it's a normal response indicating a user name, return true
 *  and store the user name at *ident_user. If it's anything else,
 *  return false.
 */
static bool
interpret_ident_response(const char *ident_response,
                         char *ident_user)
{
    const char *cursor = ident_response;    /* Cursor into *ident_response */

    /*
     * Ident's response, in the telnet tradition, should end in crlf (\r\n).
     */
    if (strlen(ident_response) < 2)
        return false;
    else if (ident_response[strlen(ident_response) - 2] != '\r')
        return false;
    else
    {
        while (*cursor != ':' && *cursor != '\r')
            cursor++;           /* skip port field */

        if (*cursor != ':')
            return false;
        else
        {
            /* We're positioned to colon before response type field */
            char        response_type[80];
            int         i;      /* Index into *response_type */

            cursor++;           /* Go over colon */
            while (pg_isblank(*cursor))
                cursor++;       /* skip blanks */
            i = 0;
            while (*cursor != ':' && *cursor != '\r' && !pg_isblank(*cursor) &&
                   i < (int) (sizeof(response_type) - 1))
                response_type[i++] = *cursor++;
            response_type[i] = '\0';
            while (pg_isblank(*cursor))
                cursor++;       /* skip blanks */
            if (strcmp(response_type, "USERID") != 0)
                return false;
            else
            {
                /*
                 * It's a USERID response.  Good.  "cursor" should be pointing
                 * to the colon that precedes the operating system type.
                 */
                if (*cursor != ':')
                    return false;
                else
                {
                    cursor++;   /* Go over colon */
                    /* Skip over operating system field. */
                    while (*cursor != ':' && *cursor != '\r')
                        cursor++;
                    if (*cursor != ':')
                        return false;
                    else
                    {
                        int         i;  /* Index into *ident_user */

                        cursor++;   /* Go over colon */
                        while (pg_isblank(*cursor))
                            cursor++;   /* skip blanks */
                        /* Rest of line is user name.  Copy it over. */
                        i = 0;
                        while (*cursor != '\r' && i < IDENT_USERNAME_MAX)
                            ident_user[i++] = *cursor++;
                        ident_user[i] = '\0';
                        return true;
                    }
                }
            }
        }
    }
}


/*
 *  Talk to the ident server on "remote_addr" and find out who
 *  owns the tcp connection to "local_addr"
 *  If the username is successfully retrieved, check the usermap.
 *
 *  XXX: Using WaitLatchOrSocket() and doing a CHECK_FOR_INTERRUPTS() if the
 *  latch was set would improve the responsiveness to timeouts/cancellations.
 */
static int
ident_inet(hbaPort *port)
{
    const SockAddr remote_addr = port->raddr;
    const SockAddr local_addr = port->laddr;
    char        ident_user[IDENT_USERNAME_MAX + 1];
    pgsocket    sock_fd = PGINVALID_SOCKET; /* for talking to Ident server */
    int         rc;             /* Return code from a locally called function */
    bool        ident_return;
    char        remote_addr_s[NI_MAXHOST];
    char        remote_port[NI_MAXSERV];
    char        local_addr_s[NI_MAXHOST];
    char        local_port[NI_MAXSERV];
    char        ident_port[NI_MAXSERV];
    char        ident_query[80];
    char        ident_response[80 + IDENT_USERNAME_MAX];
    struct addrinfo *ident_serv = NULL,
               *la = NULL,
                hints;

    /*
     * Might look a little weird to first convert it to text and then back to
     * sockaddr, but it's protocol independent.
     */
    pg_getnameinfo_all(&remote_addr.addr, remote_addr.salen,
                       remote_addr_s, sizeof(remote_addr_s),
                       remote_port, sizeof(remote_port),
                       NI_NUMERICHOST | NI_NUMERICSERV);
    pg_getnameinfo_all(&local_addr.addr, local_addr.salen,
                       local_addr_s, sizeof(local_addr_s),
                       local_port, sizeof(local_port),
                       NI_NUMERICHOST | NI_NUMERICSERV);

    snprintf(ident_port, sizeof(ident_port), "%d", IDENT_PORT);
    hints.ai_flags = AI_NUMERICHOST;
    hints.ai_family = remote_addr.addr.ss_family;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = 0;
    hints.ai_addrlen = 0;
    hints.ai_canonname = NULL;
    hints.ai_addr = NULL;
    hints.ai_next = NULL;
    rc = pg_getaddrinfo_all(remote_addr_s, ident_port, &hints, &ident_serv);
    if (rc || !ident_serv)
    {
        /* we don't expect this to happen */
        ident_return = false;
        goto ident_inet_done;
    }

    hints.ai_flags = AI_NUMERICHOST;
    hints.ai_family = local_addr.addr.ss_family;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = 0;
    hints.ai_addrlen = 0;
    hints.ai_canonname = NULL;
    hints.ai_addr = NULL;
    hints.ai_next = NULL;
    rc = pg_getaddrinfo_all(local_addr_s, NULL, &hints, &la);
    if (rc || !la)
    {
        /* we don't expect this to happen */
        ident_return = false;
        goto ident_inet_done;
    }

    sock_fd = socket(ident_serv->ai_family, ident_serv->ai_socktype,
                     ident_serv->ai_protocol);
    if (sock_fd == PGINVALID_SOCKET)
    {
        ereport(LOG,
                (errcode_for_socket_access(),
                 errmsg("could not create socket for Ident connection: %m")));
        ident_return = false;
        goto ident_inet_done;
    }

    /*
     * Bind to the address which the client originally contacted, otherwise
     * the ident server won't be able to match up the right connection. This
     * is necessary if the PostgreSQL server is running on an IP alias.
     */
    rc = bind(sock_fd, la->ai_addr, la->ai_addrlen);
    if (rc != 0)
    {
        ereport(LOG,
                (errcode_for_socket_access(),
                 errmsg("could not bind to local address \"%s\": %m",
                        local_addr_s)));
        ident_return = false;
        goto ident_inet_done;
    }

    rc = connect(sock_fd, ident_serv->ai_addr,
                 ident_serv->ai_addrlen);
    if (rc != 0)
    {
        ereport(LOG,
                (errcode_for_socket_access(),
                 errmsg("could not connect to Ident server at address \"%s\", port %s: %m",
                        remote_addr_s, ident_port)));
        ident_return = false;
        goto ident_inet_done;
    }

    /* The query we send to the Ident server */
    snprintf(ident_query, sizeof(ident_query), "%s,%s\r\n",
             remote_port, local_port);

    /* loop in case send is interrupted */
    do
    {
        CHECK_FOR_INTERRUPTS();

        rc = send(sock_fd, ident_query, strlen(ident_query), 0);
    } while (rc < 0 && errno == EINTR);

    if (rc < 0)
    {
        ereport(LOG,
                (errcode_for_socket_access(),
                 errmsg("could not send query to Ident server at address \"%s\", port %s: %m",
                        remote_addr_s, ident_port)));
        ident_return = false;
        goto ident_inet_done;
    }

    do
    {
        CHECK_FOR_INTERRUPTS();

        rc = recv(sock_fd, ident_response, sizeof(ident_response) - 1, 0);
    } while (rc < 0 && errno == EINTR);

    if (rc < 0)
    {
        ereport(LOG,
                (errcode_for_socket_access(),
                 errmsg("could not receive response from Ident server at address \"%s\", port %s: %m",
                        remote_addr_s, ident_port)));
        ident_return = false;
        goto ident_inet_done;
    }

    ident_response[rc] = '\0';
    ident_return = interpret_ident_response(ident_response, ident_user);
    if (!ident_return)
        ereport(LOG,
                (errmsg("invalidly formatted response from Ident server: \"%s\"",
                        ident_response)));

ident_inet_done:
    if (sock_fd != PGINVALID_SOCKET)
        closesocket(sock_fd);
    if (ident_serv)
        pg_freeaddrinfo_all(remote_addr.addr.ss_family, ident_serv);
    if (la)
        pg_freeaddrinfo_all(local_addr.addr.ss_family, la);

    if (ident_return)
        /* Success! Check the usermap */
        return check_usermap(port->hba->usermap, port->user_name, ident_user, false);
    return STATUS_ERROR;
}


/*----------------------------------------------------------------
 * Peer authentication system
 *----------------------------------------------------------------
 */

/*
 *  Ask kernel about the credentials of the connecting process,
 *  determine the symbolic name of the corresponding user, and check
 *  if valid per the usermap.
 *
 *  Iff authorized, return STATUS_OK, otherwise return STATUS_ERROR.
 */
static int
auth_peer(hbaPort *port)
{
    uid_t       uid;
    gid_t       gid;
#ifndef WIN32
    struct passwd *pw;
    char       *peer_user;
    int         ret;
#endif

    if (getpeereid(port->sock, &uid, &gid) != 0)
    {
        /* Provide special error message if getpeereid is a stub */
        if (errno == ENOSYS)
            ereport(LOG,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("peer authentication is not supported on this platform")));
        else
            ereport(LOG,
                    (errcode_for_socket_access(),
                     errmsg("could not get peer credentials: %m")));
        return STATUS_ERROR;
    }

#ifndef WIN32
    errno = 0;                  /* clear errno before call */
    pw = getpwuid(uid);
    if (!pw)
    {
        int         save_errno = errno;

        ereport(LOG,
                (errmsg("could not look up local user ID %ld: %s",
                        (long) uid,
                        save_errno ? strerror(save_errno) : _("user does not exist"))));
        return STATUS_ERROR;
    }

    /* Make a copy of static getpw*() result area. */
    peer_user = pstrdup(pw->pw_name);

    ret = check_usermap(port->hba->usermap, port->user_name, peer_user, false);

    pfree(peer_user);

    return ret;
#else
    /* should have failed with ENOSYS above */
    Assert(false);
    return STATUS_ERROR;
#endif
}


/*----------------------------------------------------------------
 * PAM authentication system
 *----------------------------------------------------------------
 */
#ifdef USE_PAM

/*
 * PAM conversation function
 */

static int
pam_passwd_conv_proc(int num_msg, const struct pam_message **msg,
                     struct pam_response **resp, void *appdata_ptr)
{
    const char *passwd;
    struct pam_response *reply;
    int         i;

    if (appdata_ptr)
        passwd = (char *) appdata_ptr;
    else
    {
        /*
         * Workaround for Solaris 2.6 where the PAM library is broken and does
         * not pass appdata_ptr to the conversation routine
         */
        passwd = pam_passwd;
    }

    *resp = NULL;               /* in case of error exit */

    if (num_msg <= 0 || num_msg > PAM_MAX_NUM_MSG)
        return PAM_CONV_ERR;

    /*
     * Explicitly not using palloc here - PAM will free this memory in
     * pam_end()
     */
    if ((reply = calloc(num_msg, sizeof(struct pam_response))) == NULL)
    {
        ereport(LOG,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory")));
        return PAM_CONV_ERR;
    }

    for (i = 0; i < num_msg; i++)
    {
        switch (msg[i]->msg_style)
        {
            case PAM_PROMPT_ECHO_OFF:
                if (strlen(passwd) == 0)
                {
                    /*
                     * Password wasn't passed to PAM the first time around -
                     * let's go ask the client to send a password, which we
                     * then stuff into PAM.
                     */
                    sendAuthRequest(pam_port_cludge, AUTH_REQ_PASSWORD, NULL, 0);
                    passwd = recv_password_packet(pam_port_cludge);
                    if (passwd == NULL)
                    {
                        /*
                         * Client didn't want to send password.  We
                         * intentionally do not log anything about this,
                         * either here or at higher levels.
                         */
                        pam_no_password = true;
                        goto fail;
                    }
                }
                if ((reply[i].resp = strdup(passwd)) == NULL)
                    goto fail;
                reply[i].resp_retcode = PAM_SUCCESS;
                break;
            case PAM_ERROR_MSG:
                ereport(LOG,
                        (errmsg("error from underlying PAM layer: %s",
                                msg[i]->msg)));
                /* FALL THROUGH */
            case PAM_TEXT_INFO:
                /* we don't bother to log TEXT_INFO messages */
                if ((reply[i].resp = strdup("")) == NULL)
                    goto fail;
                reply[i].resp_retcode = PAM_SUCCESS;
                break;
            default:
                ereport(LOG,
                        (errmsg("unsupported PAM conversation %d/\"%s\"",
                                msg[i]->msg_style,
                                msg[i]->msg ? msg[i]->msg : "(none)")));
                goto fail;
        }
    }

    *resp = reply;
    return PAM_SUCCESS;

fail:
    /* free up whatever we allocated */
    for (i = 0; i < num_msg; i++)
    {
        if (reply[i].resp != NULL)
            free(reply[i].resp);
    }
    free(reply);

    return PAM_CONV_ERR;
}


/*
 * Check authentication against PAM.
 */
static int
CheckPAMAuth(Port *port, const char *user, const char *password)
{
    int         retval;
    pam_handle_t *pamh = NULL;

    /*
     * We can't entirely rely on PAM to pass through appdata --- it appears
     * not to work on at least Solaris 2.6.  So use these ugly static
     * variables instead.
     */
    pam_passwd = password;
    pam_port_cludge = port;
    pam_no_password = false;

    /*
     * Set the application data portion of the conversation struct.  This is
     * later used inside the PAM conversation to pass the password to the
     * authentication module.
     */
    pam_passw_conv.appdata_ptr = unconstify(char *, password);  /* from password above,
                                                                 * not allocated */

    /* Optionally, one can set the service name in pg_hba.conf */
    if (port->hba->pamservice && port->hba->pamservice[0] != '\0')
        retval = pam_start(port->hba->pamservice, "pgsql@",
                           &pam_passw_conv, &pamh);
    else
        retval = pam_start(PGSQL_PAM_SERVICE, "pgsql@",
                           &pam_passw_conv, &pamh);

    if (retval != PAM_SUCCESS)
    {
        ereport(LOG,
                (errmsg("could not create PAM authenticator: %s",
                        pam_strerror(pamh, retval))));
        pam_passwd = NULL;      /* Unset pam_passwd */
        return STATUS_ERROR;
    }

    retval = pam_set_item(pamh, PAM_USER, user);

    if (retval != PAM_SUCCESS)
    {
        ereport(LOG,
                (errmsg("pam_set_item(PAM_USER) failed: %s",
                        pam_strerror(pamh, retval))));
        pam_passwd = NULL;      /* Unset pam_passwd */
        return STATUS_ERROR;
    }

    if (port->hba->conntype != ctLocal)
    {
        char        hostinfo[NI_MAXHOST];
        int         flags;

        if (port->hba->pam_use_hostname)
            flags = 0;
        else
            flags = NI_NUMERICHOST | NI_NUMERICSERV;

        retval = pg_getnameinfo_all(&port->raddr.addr, port->raddr.salen,
                                    hostinfo, sizeof(hostinfo), NULL, 0,
                                    flags);
        if (retval != 0)
        {
            ereport(WARNING,
                    (errmsg_internal("pg_getnameinfo_all() failed: %s",
                                     gai_strerror(retval))));
            return STATUS_ERROR;
        }

        retval = pam_set_item(pamh, PAM_RHOST, hostinfo);

        if (retval != PAM_SUCCESS)
        {
            ereport(LOG,
                    (errmsg("pam_set_item(PAM_RHOST) failed: %s",
                            pam_strerror(pamh, retval))));
            pam_passwd = NULL;
            return STATUS_ERROR;
        }
    }

    retval = pam_set_item(pamh, PAM_CONV, &pam_passw_conv);

    if (retval != PAM_SUCCESS)
    {
        ereport(LOG,
                (errmsg("pam_set_item(PAM_CONV) failed: %s",
                        pam_strerror(pamh, retval))));
        pam_passwd = NULL;      /* Unset pam_passwd */
        return STATUS_ERROR;
    }

    retval = pam_authenticate(pamh, 0);

    if (retval != PAM_SUCCESS)
    {
        /* If pam_passwd_conv_proc saw EOF, don't log anything */
        if (!pam_no_password)
            ereport(LOG,
                    (errmsg("pam_authenticate failed: %s",
                            pam_strerror(pamh, retval))));
        pam_passwd = NULL;      /* Unset pam_passwd */
        return pam_no_password ? STATUS_EOF : STATUS_ERROR;
    }

    retval = pam_acct_mgmt(pamh, 0);

    if (retval != PAM_SUCCESS)
    {
        /* If pam_passwd_conv_proc saw EOF, don't log anything */
        if (!pam_no_password)
            ereport(LOG,
                    (errmsg("pam_acct_mgmt failed: %s",
                            pam_strerror(pamh, retval))));
        pam_passwd = NULL;      /* Unset pam_passwd */
        return pam_no_password ? STATUS_EOF : STATUS_ERROR;
    }

    retval = pam_end(pamh, retval);

    if (retval != PAM_SUCCESS)
    {
        ereport(LOG,
                (errmsg("could not release PAM authenticator: %s",
                        pam_strerror(pamh, retval))));
    }

    pam_passwd = NULL;          /* Unset pam_passwd */

    return (retval == PAM_SUCCESS ? STATUS_OK : STATUS_ERROR);
}
#endif                          /* USE_PAM */


/*----------------------------------------------------------------
 * BSD authentication system
 *----------------------------------------------------------------
 */
#ifdef USE_BSD_AUTH
static int
CheckBSDAuth(Port *port, char *user)
{
    char       *passwd;
    int         retval;

    /* Send regular password request to client, and get the response */
    sendAuthRequest(port, AUTH_REQ_PASSWORD, NULL, 0);

    passwd = recv_password_packet(port);
    if (passwd == NULL)
        return STATUS_EOF;

    /*
     * Ask the BSD auth system to verify password.  Note that auth_userokay
     * will overwrite the password string with zeroes, but it's just a
     * temporary string so we don't care.
     */
    retval = auth_userokay(user, NULL, "auth-postgresql", passwd);

    pfree(passwd);

    if (!retval)
        return STATUS_ERROR;

    return STATUS_OK;
}
#endif                          /* USE_BSD_AUTH */


/*----------------------------------------------------------------
 * LDAP authentication system
 *----------------------------------------------------------------
 */
#ifdef USE_LDAP

static int  errdetail_for_ldap(LDAP *ldap);

/*
 * Initialize a connection to the LDAP server, including setting up
 * TLS if requested.
 */
static int
InitializeLDAPConnection(Port *port, LDAP **ldap)
{
    const char *scheme;
    int         ldapversion = LDAP_VERSION3;
    int         r;

    scheme = port->hba->ldapscheme;
    if (scheme == NULL)
        scheme = "ldap";
#ifdef WIN32
    if (strcmp(scheme, "ldaps") == 0)
        *ldap = ldap_sslinit(port->hba->ldapserver, port->hba->ldapport, 1);
    else
        *ldap = ldap_init(port->hba->ldapserver, port->hba->ldapport);
    if (!*ldap)
    {
        ereport(LOG,
                (errmsg("could not initialize LDAP: error code %d",
                        (int) LdapGetLastError())));

        return STATUS_ERROR;
    }
#else
#ifdef HAVE_LDAP_INITIALIZE

    /*
     * OpenLDAP provides a non-standard extension ldap_initialize() that takes
     * a list of URIs, allowing us to request "ldaps" instead of "ldap".  It
     * also provides ldap_domain2hostlist() to find LDAP servers automatically
     * using DNS SRV.  They were introduced in the same version, so for now we
     * don't have an extra configure check for the latter.
     */
    {
        StringInfoData uris;
        char       *hostlist = NULL;
        char       *p;
        bool        append_port;

        /* We'll build a space-separated scheme://hostname:port list here */
        initStringInfo(&uris);

        /*
         * If pg_hba.conf provided no hostnames, we can ask OpenLDAP to try to
         * find some by extracting a domain name from the base DN and looking
         * up DSN SRV records for _ldap._tcp.<domain>.
         */
        if (!port->hba->ldapserver || port->hba->ldapserver[0] == '\0')
        {
            char       *domain;

            /* ou=blah,dc=foo,dc=bar -> foo.bar */
            if (ldap_dn2domain(port->hba->ldapbasedn, &domain))
            {
                ereport(LOG,
                        (errmsg("could not extract domain name from ldapbasedn")));
                return STATUS_ERROR;
            }

            /* Look up a list of LDAP server hosts and port numbers */
            if (ldap_domain2hostlist(domain, &hostlist))
            {
                ereport(LOG,
                        (errmsg("LDAP authentication could not find DNS SRV records for \"%s\"",
                                domain),
                         (errhint("Set an LDAP server name explicitly."))));
                ldap_memfree(domain);
                return STATUS_ERROR;
            }
            ldap_memfree(domain);

            /* We have a space-separated list of host:port entries */
            p = hostlist;
            append_port = false;
        }
        else
        {
            /* We have a space-separated list of hosts from pg_hba.conf */
            p = port->hba->ldapserver;
            append_port = true;
        }

        /* Convert the list of host[:port] entries to full URIs */
        do
        {
            size_t      size;

            /* Find the span of the next entry */
            size = strcspn(p, " ");

            /* Append a space separator if this isn't the first URI */
            if (uris.len > 0)
                appendStringInfoChar(&uris, ' ');

            /* Append scheme://host:port */
            appendStringInfoString(&uris, scheme);
            appendStringInfoString(&uris, "://");
            appendBinaryStringInfo(&uris, p, size);
            if (append_port)
                appendStringInfo(&uris, ":%d", port->hba->ldapport);

            /* Step over this entry and any number of trailing spaces */
            p += size;
            while (*p == ' ')
                ++p;
        } while (*p);

        /* Free memory from OpenLDAP if we looked up SRV records */
        if (hostlist)
            ldap_memfree(hostlist);

        /* Finally, try to connect using the URI list */
        r = ldap_initialize(ldap, uris.data);
        pfree(uris.data);
        if (r != LDAP_SUCCESS)
        {
            ereport(LOG,
                    (errmsg("could not initialize LDAP: %s",
                            ldap_err2string(r))));

            return STATUS_ERROR;
        }
    }
#else
    if (strcmp(scheme, "ldaps") == 0)
    {
        ereport(LOG,
                (errmsg("ldaps not supported with this LDAP library")));

        return STATUS_ERROR;
    }
    *ldap = ldap_init(port->hba->ldapserver, port->hba->ldapport);
    if (!*ldap)
    {
        ereport(LOG,
                (errmsg("could not initialize LDAP: %m")));

        return STATUS_ERROR;
    }
#endif
#endif

    if ((r = ldap_set_option(*ldap, LDAP_OPT_PROTOCOL_VERSION, &ldapversion)) != LDAP_SUCCESS)
    {
        ereport(LOG,
                (errmsg("could not set LDAP protocol version: %s",
                        ldap_err2string(r)),
                 errdetail_for_ldap(*ldap)));
        ldap_unbind(*ldap);
        return STATUS_ERROR;
    }

    if (port->hba->ldaptls)
    {
#ifndef WIN32
        if ((r = ldap_start_tls_s(*ldap, NULL, NULL)) != LDAP_SUCCESS)
#else
        static __ldap_start_tls_sA _ldap_start_tls_sA = NULL;

        if (_ldap_start_tls_sA == NULL)
        {
            /*
             * Need to load this function dynamically because it may not exist
             * on Windows, and causes a load error for the whole exe if
             * referenced.
             */
            HANDLE      ldaphandle;

            ldaphandle = LoadLibrary("WLDAP32.DLL");
            if (ldaphandle == NULL)
            {
                /*
                 * should never happen since we import other files from
                 * wldap32, but check anyway
                 */
                ereport(LOG,
                        (errmsg("could not load library \"%s\": error code %lu",
                                "WLDAP32.DLL", GetLastError())));
                ldap_unbind(*ldap);
                return STATUS_ERROR;
            }
            _ldap_start_tls_sA = (__ldap_start_tls_sA) (pg_funcptr_t) GetProcAddress(ldaphandle, "ldap_start_tls_sA");
            if (_ldap_start_tls_sA == NULL)
            {
                ereport(LOG,
                        (errmsg("could not load function _ldap_start_tls_sA in wldap32.dll"),
                         errdetail("LDAP over SSL is not supported on this platform.")));
                ldap_unbind(*ldap);
                FreeLibrary(ldaphandle);
                return STATUS_ERROR;
            }

            /*
             * Leak LDAP handle on purpose, because we need the library to
             * stay open. This is ok because it will only ever be leaked once
             * per process and is automatically cleaned up on process exit.
             */
        }
        if ((r = _ldap_start_tls_sA(*ldap, NULL, NULL, NULL, NULL)) != LDAP_SUCCESS)
#endif
        {
            ereport(LOG,
                    (errmsg("could not start LDAP TLS session: %s",
                            ldap_err2string(r)),
                     errdetail_for_ldap(*ldap)));
            ldap_unbind(*ldap);
            return STATUS_ERROR;
        }
    }

    return STATUS_OK;
}

/* Placeholders recognized by FormatSearchFilter.  For now just one. */
#define LPH_USERNAME "$username"
#define LPH_USERNAME_LEN (sizeof(LPH_USERNAME) - 1)

/* Not all LDAP implementations define this. */
#ifndef LDAP_NO_ATTRS
#define LDAP_NO_ATTRS "1.1"
#endif

/* Not all LDAP implementations define this. */
#ifndef LDAPS_PORT
#define LDAPS_PORT 636
#endif

/*
 * Return a newly allocated C string copied from "pattern" with all
 * occurrences of the placeholder "$username" replaced with "user_name".
 */
static char *
FormatSearchFilter(const char *pattern, const char *user_name)
{
    StringInfoData output;

    initStringInfo(&output);
    while (*pattern != '\0')
    {
        if (strncmp(pattern, LPH_USERNAME, LPH_USERNAME_LEN) == 0)
        {
            appendStringInfoString(&output, user_name);
            pattern += LPH_USERNAME_LEN;
        }
        else
            appendStringInfoChar(&output, *pattern++);
    }

    return output.data;
}

/*
 * Perform LDAP authentication
 */
static int
CheckLDAPAuth(Port *port)
{
    char       *passwd;
    LDAP       *ldap;
    int         r;
    char       *fulluser;
    const char *server_name;

#ifdef HAVE_LDAP_INITIALIZE

    /*
     * For OpenLDAP, allow empty hostname if we have a basedn.  We'll look for
     * servers with DNS SRV records via OpenLDAP library facilities.
     */
    if ((!port->hba->ldapserver || port->hba->ldapserver[0] == '\0') &&
        (!port->hba->ldapbasedn || port->hba->ldapbasedn[0] == '\0'))
    {
        ereport(LOG,
                (errmsg("LDAP server not specified, and no ldapbasedn")));
        return STATUS_ERROR;
    }
#else
    if (!port->hba->ldapserver || port->hba->ldapserver[0] == '\0')
    {
        ereport(LOG,
                (errmsg("LDAP server not specified")));
        return STATUS_ERROR;
    }
#endif

    /*
     * If we're using SRV records, we don't have a server name so we'll just
     * show an empty string in error messages.
     */
    server_name = port->hba->ldapserver ? port->hba->ldapserver : "";

    if (port->hba->ldapport == 0)
    {
        if (port->hba->ldapscheme != NULL &&
            strcmp(port->hba->ldapscheme, "ldaps") == 0)
            port->hba->ldapport = LDAPS_PORT;
        else
            port->hba->ldapport = LDAP_PORT;
    }

    sendAuthRequest(port, AUTH_REQ_PASSWORD, NULL, 0);

    passwd = recv_password_packet(port);
    if (passwd == NULL)
        return STATUS_EOF;      /* client wouldn't send password */

    if (InitializeLDAPConnection(port, &ldap) == STATUS_ERROR)
    {
        /* Error message already sent */
        pfree(passwd);
        return STATUS_ERROR;
    }

    if (port->hba->ldapbasedn)
    {
        /*
         * First perform an LDAP search to find the DN for the user we are
         * trying to log in as.
         */
        char       *filter;
        LDAPMessage *search_message;
        LDAPMessage *entry;
        char       *attributes[] = {LDAP_NO_ATTRS, NULL};
        char       *dn;
        char       *c;
        int         count;

        /*
         * Disallow any characters that we would otherwise need to escape,
         * since they aren't really reasonable in a username anyway. Allowing
         * them would make it possible to inject any kind of custom filters in
         * the LDAP filter.
         */
        for (c = port->user_name; *c; c++)
        {
            if (*c == '*' ||
                *c == '(' ||
                *c == ')' ||
                *c == '\\' ||
                *c == '/')
            {
                ereport(LOG,
                        (errmsg("invalid character in user name for LDAP authentication")));
                ldap_unbind(ldap);
                pfree(passwd);
                return STATUS_ERROR;
            }
        }

        /*
         * Bind with a pre-defined username/password (if available) for
         * searching. If none is specified, this turns into an anonymous bind.
         */
        r = ldap_simple_bind_s(ldap,
                               port->hba->ldapbinddn ? port->hba->ldapbinddn : "",
                               port->hba->ldapbindpasswd ? port->hba->ldapbindpasswd : "");
        if (r != LDAP_SUCCESS)
        {
            ereport(LOG,
                    (errmsg("could not perform initial LDAP bind for ldapbinddn \"%s\" on server \"%s\": %s",
                            port->hba->ldapbinddn ? port->hba->ldapbinddn : "",
                            server_name,
                            ldap_err2string(r)),
                     errdetail_for_ldap(ldap)));
            ldap_unbind(ldap);
            pfree(passwd);
            return STATUS_ERROR;
        }

        /* Build a custom filter or a single attribute filter? */
        if (port->hba->ldapsearchfilter)
            filter = FormatSearchFilter(port->hba->ldapsearchfilter, port->user_name);
        else if (port->hba->ldapsearchattribute)
            filter = psprintf("(%s=%s)", port->hba->ldapsearchattribute, port->user_name);
        else
            filter = psprintf("(uid=%s)", port->user_name);

        r = ldap_search_s(ldap,
                          port->hba->ldapbasedn,
                          port->hba->ldapscope,
                          filter,
                          attributes,
                          0,
                          &search_message);

        if (r != LDAP_SUCCESS)
        {
            ereport(LOG,
                    (errmsg("could not search LDAP for filter \"%s\" on server \"%s\": %s",
                            filter, server_name, ldap_err2string(r)),
                     errdetail_for_ldap(ldap)));
            ldap_unbind(ldap);
            pfree(passwd);
            pfree(filter);
            return STATUS_ERROR;
        }

        count = ldap_count_entries(ldap, search_message);
        if (count != 1)
        {
            if (count == 0)
                ereport(LOG,
                        (errmsg("LDAP user \"%s\" does not exist", port->user_name),
                         errdetail("LDAP search for filter \"%s\" on server \"%s\" returned no entries.",
                                   filter, server_name)));
            else
                ereport(LOG,
                        (errmsg("LDAP user \"%s\" is not unique", port->user_name),
                         errdetail_plural("LDAP search for filter \"%s\" on server \"%s\" returned %d entry.",
                                          "LDAP search for filter \"%s\" on server \"%s\" returned %d entries.",
                                          count,
                                          filter, server_name, count)));

            ldap_unbind(ldap);
            pfree(passwd);
            pfree(filter);
            ldap_msgfree(search_message);
            return STATUS_ERROR;
        }

        entry = ldap_first_entry(ldap, search_message);
        dn = ldap_get_dn(ldap, entry);
        if (dn == NULL)
        {
            int         error;

            (void) ldap_get_option(ldap, LDAP_OPT_ERROR_NUMBER, &error);
            ereport(LOG,
                    (errmsg("could not get dn for the first entry matching \"%s\" on server \"%s\": %s",
                            filter, server_name,
                            ldap_err2string(error)),
                     errdetail_for_ldap(ldap)));
            ldap_unbind(ldap);
            pfree(passwd);
            pfree(filter);
            ldap_msgfree(search_message);
            return STATUS_ERROR;
        }
        fulluser = pstrdup(dn);

        pfree(filter);
        ldap_memfree(dn);
        ldap_msgfree(search_message);

        /* Unbind and disconnect from the LDAP server */
        r = ldap_unbind_s(ldap);
        if (r != LDAP_SUCCESS)
        {
            ereport(LOG,
                    (errmsg("could not unbind after searching for user \"%s\" on server \"%s\"",
                            fulluser, server_name)));
            pfree(passwd);
            pfree(fulluser);
            return STATUS_ERROR;
        }

        /*
         * Need to re-initialize the LDAP connection, so that we can bind to
         * it with a different username.
         */
        if (InitializeLDAPConnection(port, &ldap) == STATUS_ERROR)
        {
            pfree(passwd);
            pfree(fulluser);

            /* Error message already sent */
            return STATUS_ERROR;
        }
    }
    else
        fulluser = psprintf("%s%s%s",
                            port->hba->ldapprefix ? port->hba->ldapprefix : "",
                            port->user_name,
                            port->hba->ldapsuffix ? port->hba->ldapsuffix : "");

    r = ldap_simple_bind_s(ldap, fulluser, passwd);

    if (r != LDAP_SUCCESS)
    {
        ereport(LOG,
                (errmsg("LDAP login failed for user \"%s\" on server \"%s\": %s",
                        fulluser, server_name, ldap_err2string(r)),
                 errdetail_for_ldap(ldap)));
        ldap_unbind(ldap);
        pfree(passwd);
        pfree(fulluser);
        return STATUS_ERROR;
    }

    ldap_unbind(ldap);
    pfree(passwd);
    pfree(fulluser);

    return STATUS_OK;
}

/*
 * Add a detail error message text to the current error if one can be
 * constructed from the LDAP 'diagnostic message'.
 */
static int
errdetail_for_ldap(LDAP *ldap)
{
    char       *message;
    int         rc;

    rc = ldap_get_option(ldap, LDAP_OPT_DIAGNOSTIC_MESSAGE, &message);
    if (rc == LDAP_SUCCESS && message != NULL)
    {
        errdetail("LDAP diagnostics: %s", message);
        ldap_memfree(message);
    }

    return 0;
}

#endif                          /* USE_LDAP */


/*----------------------------------------------------------------
 * SSL client certificate authentication
 *----------------------------------------------------------------
 */
#ifdef USE_SSL
static int
CheckCertAuth(Port *port)
{
    int         status_check_usermap = STATUS_ERROR;

    Assert(port->ssl);

    /* Make sure we have received a username in the certificate */
    if (port->peer_cn == NULL ||
        strlen(port->peer_cn) <= 0)
    {
        ereport(LOG,
                (errmsg("certificate authentication failed for user \"%s\": client certificate contains no user name",
                        port->user_name)));
        return STATUS_ERROR;
    }

    /* Just pass the certificate cn to the usermap check */
    status_check_usermap = check_usermap(port->hba->usermap, port->user_name, port->peer_cn, false);
    if (status_check_usermap != STATUS_OK)
    {
        /*
         * If clientcert=verify-full was specified and the authentication
         * method is other than uaCert, log the reason for rejecting the
         * authentication.
         */
        if (port->hba->clientcert == clientCertFull && port->hba->auth_method != uaCert)
        {
            ereport(LOG,
                    (errmsg("certificate validation (clientcert=verify-full) failed for user \"%s\": CN mismatch",
                            port->user_name)));
        }
    }
    return status_check_usermap;
}
#endif


/*----------------------------------------------------------------
 * RADIUS authentication
 *----------------------------------------------------------------
 */

/*
 * RADIUS authentication is described in RFC2865 (and several others).
 */

#define RADIUS_VECTOR_LENGTH 16
#define RADIUS_HEADER_LENGTH 20
#define RADIUS_MAX_PASSWORD_LENGTH 128

/* Maximum size of a RADIUS packet we will create or accept */
#define RADIUS_BUFFER_SIZE 1024

typedef struct
{
    uint8       attribute;
    uint8       length;
    uint8       data[FLEXIBLE_ARRAY_MEMBER];
} radius_attribute;

typedef struct
{
    uint8       code;
    uint8       id;
    uint16      length;
    uint8       vector[RADIUS_VECTOR_LENGTH];
    /* this is a bit longer than strictly necessary: */
    char        pad[RADIUS_BUFFER_SIZE - RADIUS_VECTOR_LENGTH];
} radius_packet;

/* RADIUS packet types */
#define RADIUS_ACCESS_REQUEST   1
#define RADIUS_ACCESS_ACCEPT    2
#define RADIUS_ACCESS_REJECT    3

/* RADIUS attributes */
#define RADIUS_USER_NAME        1
#define RADIUS_PASSWORD         2
#define RADIUS_SERVICE_TYPE     6
#define RADIUS_NAS_IDENTIFIER   32

/* RADIUS service types */
#define RADIUS_AUTHENTICATE_ONLY    8

/* Seconds to wait - XXX: should be in a config variable! */
#define RADIUS_TIMEOUT 3

static void
radius_add_attribute(radius_packet *packet, uint8 type, const unsigned char *data, int len)
{
    radius_attribute *attr;

    if (packet->length + len > RADIUS_BUFFER_SIZE)
    {
        /*
         * With remotely realistic data, this can never happen. But catch it
         * just to make sure we don't overrun a buffer. We'll just skip adding
         * the broken attribute, which will in the end cause authentication to
         * fail.
         */
        elog(WARNING,
             "adding attribute code %d with length %d to radius packet would create oversize packet, ignoring",
             type, len);
        return;
    }

    attr = (radius_attribute *) ((unsigned char *) packet + packet->length);
    attr->attribute = type;
    attr->length = len + 2;     /* total size includes type and length */
    memcpy(attr->data, data, len);
    packet->length += attr->length;
}

static int
CheckRADIUSAuth(Port *port)
{
    char       *passwd;
    ListCell   *server,
               *secrets,
               *radiusports,
               *identifiers;

    /* Make sure struct alignment is correct */
    Assert(offsetof(radius_packet, vector) == 4);

    /* Verify parameters */
    if (list_length(port->hba->radiusservers) < 1)
    {
        ereport(LOG,
                (errmsg("RADIUS server not specified")));
        return STATUS_ERROR;
    }

    if (list_length(port->hba->radiussecrets) < 1)
    {
        ereport(LOG,
                (errmsg("RADIUS secret not specified")));
        return STATUS_ERROR;
    }

    /* Send regular password request to client, and get the response */
    sendAuthRequest(port, AUTH_REQ_PASSWORD, NULL, 0);

    passwd = recv_password_packet(port);
    if (passwd == NULL)
        return STATUS_EOF;      /* client wouldn't send password */

    if (strlen(passwd) > RADIUS_MAX_PASSWORD_LENGTH)
    {
        ereport(LOG,
                (errmsg("RADIUS authentication does not support passwords longer than %d characters", RADIUS_MAX_PASSWORD_LENGTH)));
        pfree(passwd);
        return STATUS_ERROR;
    }

    /*
     * Loop over and try each server in order.
     */
    secrets = list_head(port->hba->radiussecrets);
    radiusports = list_head(port->hba->radiusports);
    identifiers = list_head(port->hba->radiusidentifiers);
    foreach(server, port->hba->radiusservers)
    {
        int         ret = PerformRadiusTransaction(lfirst(server),
                                                   lfirst(secrets),
                                                   radiusports ? lfirst(radiusports) : NULL,
                                                   identifiers ? lfirst(identifiers) : NULL,
                                                   port->user_name,
                                                   passwd);

        /*------
         * STATUS_OK = Login OK
         * STATUS_ERROR = Login not OK, but try next server
         * STATUS_EOF = Login not OK, and don't try next server
         *------
         */
        if (ret == STATUS_OK)
        {
            pfree(passwd);
            return STATUS_OK;
        }
        else if (ret == STATUS_EOF)
        {
            pfree(passwd);
            return STATUS_ERROR;
        }

        /*
         * secret, port and identifiers either have length 0 (use default),
         * length 1 (use the same everywhere) or the same length as servers.
         * So if the length is >1, we advance one step. In other cases, we
         * don't and will then reuse the correct value.
         */
        if (list_length(port->hba->radiussecrets) > 1)
            secrets = lnext(port->hba->radiussecrets, secrets);
        if (list_length(port->hba->radiusports) > 1)
            radiusports = lnext(port->hba->radiusports, radiusports);
        if (list_length(port->hba->radiusidentifiers) > 1)
            identifiers = lnext(port->hba->radiusidentifiers, identifiers);
    }

    /* No servers left to try, so give up */
    pfree(passwd);
    return STATUS_ERROR;
}

static int
PerformRadiusTransaction(const char *server, const char *secret, const char *portstr, const char *identifier, const char *user_name, const char *passwd)
{
    radius_packet radius_send_pack;
    radius_packet radius_recv_pack;
    radius_packet *packet = &radius_send_pack;
    radius_packet *receivepacket = &radius_recv_pack;
    char       *radius_buffer = (char *) &radius_send_pack;
    char       *receive_buffer = (char *) &radius_recv_pack;
    int32       service = pg_hton32(RADIUS_AUTHENTICATE_ONLY);
    uint8      *cryptvector;
    int         encryptedpasswordlen;
    uint8       encryptedpassword[RADIUS_MAX_PASSWORD_LENGTH];
    uint8      *md5trailer;
    int         packetlength;
    pgsocket    sock;

#ifdef HAVE_IPV6
    struct sockaddr_in6 localaddr;
    struct sockaddr_in6 remoteaddr;
#else
    struct sockaddr_in localaddr;
    struct sockaddr_in remoteaddr;
#endif
    struct addrinfo hint;
    struct addrinfo *serveraddrs;
    int         port;
    ACCEPT_TYPE_ARG3 addrsize;
    fd_set      fdset;
    struct timeval endtime;
    int         i,
                j,
                r;

    /* Assign default values */
    if (portstr == NULL)
        portstr = "1812";
    if (identifier == NULL)
        identifier = "postgresql";

    MemSet(&hint, 0, sizeof(hint));
    hint.ai_socktype = SOCK_DGRAM;
    hint.ai_family = AF_UNSPEC;
    port = atoi(portstr);

    r = pg_getaddrinfo_all(server, portstr, &hint, &serveraddrs);
    if (r || !serveraddrs)
    {
        ereport(LOG,
                (errmsg("could not translate RADIUS server name \"%s\" to address: %s",
                        server, gai_strerror(r))));
        if (serveraddrs)
            pg_freeaddrinfo_all(hint.ai_family, serveraddrs);
        return STATUS_ERROR;
    }
    /* XXX: add support for multiple returned addresses? */

    /* Construct RADIUS packet */
    packet->code = RADIUS_ACCESS_REQUEST;
    packet->length = RADIUS_HEADER_LENGTH;
    if (!pg_strong_random(packet->vector, RADIUS_VECTOR_LENGTH))
    {
        ereport(LOG,
                (errmsg("could not generate random encryption vector")));
        pg_freeaddrinfo_all(hint.ai_family, serveraddrs);
        return STATUS_ERROR;
    }
    packet->id = packet->vector[0];
    radius_add_attribute(packet, RADIUS_SERVICE_TYPE, (const unsigned char *) &service, sizeof(service));
    radius_add_attribute(packet, RADIUS_USER_NAME, (const unsigned char *) user_name, strlen(user_name));
    radius_add_attribute(packet, RADIUS_NAS_IDENTIFIER, (const unsigned char *) identifier, strlen(identifier));

    /*
     * RADIUS password attributes are calculated as: e[0] = p[0] XOR
     * MD5(secret + Request Authenticator) for the first group of 16 octets,
     * and then: e[i] = p[i] XOR MD5(secret + e[i-1]) for the following ones
     * (if necessary)
     */
    encryptedpasswordlen = ((strlen(passwd) + RADIUS_VECTOR_LENGTH - 1) / RADIUS_VECTOR_LENGTH) * RADIUS_VECTOR_LENGTH;
    cryptvector = palloc(strlen(secret) + RADIUS_VECTOR_LENGTH);
    memcpy(cryptvector, secret, strlen(secret));

    /* for the first iteration, we use the Request Authenticator vector */
    md5trailer = packet->vector;
    for (i = 0; i < encryptedpasswordlen; i += RADIUS_VECTOR_LENGTH)
    {
        memcpy(cryptvector + strlen(secret), md5trailer, RADIUS_VECTOR_LENGTH);

        /*
         * .. and for subsequent iterations the result of the previous XOR
         * (calculated below)
         */
        md5trailer = encryptedpassword + i;

        if (!pg_md5_binary(cryptvector, strlen(secret) + RADIUS_VECTOR_LENGTH, encryptedpassword + i))
        {
            ereport(LOG,
                    (errmsg("could not perform MD5 encryption of password")));
            pfree(cryptvector);
            pg_freeaddrinfo_all(hint.ai_family, serveraddrs);
            return STATUS_ERROR;
        }

        for (j = i; j < i + RADIUS_VECTOR_LENGTH; j++)
        {
            if (j < strlen(passwd))
                encryptedpassword[j] = passwd[j] ^ encryptedpassword[j];
            else
                encryptedpassword[j] = '\0' ^ encryptedpassword[j];
        }
    }
    pfree(cryptvector);

    radius_add_attribute(packet, RADIUS_PASSWORD, encryptedpassword, encryptedpasswordlen);

    /* Length needs to be in network order on the wire */
    packetlength = packet->length;
    packet->length = pg_hton16(packet->length);

    sock = socket(serveraddrs[0].ai_family, SOCK_DGRAM, 0);
    if (sock == PGINVALID_SOCKET)
    {
        ereport(LOG,
                (errmsg("could not create RADIUS socket: %m")));
        pg_freeaddrinfo_all(hint.ai_family, serveraddrs);
        return STATUS_ERROR;
    }

    memset(&localaddr, 0, sizeof(localaddr));
#ifdef HAVE_IPV6
    localaddr.sin6_family = serveraddrs[0].ai_family;
    localaddr.sin6_addr = in6addr_any;
    if (localaddr.sin6_family == AF_INET6)
        addrsize = sizeof(struct sockaddr_in6);
    else
        addrsize = sizeof(struct sockaddr_in);
#else
    localaddr.sin_family = serveraddrs[0].ai_family;
    localaddr.sin_addr.s_addr = INADDR_ANY;
    addrsize = sizeof(struct sockaddr_in);
#endif

    if (bind(sock, (struct sockaddr *) &localaddr, addrsize))
    {
        ereport(LOG,
                (errmsg("could not bind local RADIUS socket: %m")));
        closesocket(sock);
        pg_freeaddrinfo_all(hint.ai_family, serveraddrs);
        return STATUS_ERROR;
    }

    if (sendto(sock, radius_buffer, packetlength, 0,
               serveraddrs[0].ai_addr, serveraddrs[0].ai_addrlen) < 0)
    {
        ereport(LOG,
                (errmsg("could not send RADIUS packet: %m")));
        closesocket(sock);
        pg_freeaddrinfo_all(hint.ai_family, serveraddrs);
        return STATUS_ERROR;
    }

    /* Don't need the server address anymore */
    pg_freeaddrinfo_all(hint.ai_family, serveraddrs);

    /*
     * Figure out at what time we should time out. We can't just use a single
     * call to select() with a timeout, since somebody can be sending invalid
     * packets to our port thus causing us to retry in a loop and never time
     * out.
     *
     * XXX: Using WaitLatchOrSocket() and doing a CHECK_FOR_INTERRUPTS() if
     * the latch was set would improve the responsiveness to
     * timeouts/cancellations.
     */
    gettimeofday(&endtime, NULL);
    endtime.tv_sec += RADIUS_TIMEOUT;

    while (true)
    {
        struct timeval timeout;
        struct timeval now;
        int64       timeoutval;

        gettimeofday(&now, NULL);
        timeoutval = (endtime.tv_sec * 1000000 + endtime.tv_usec) - (now.tv_sec * 1000000 + now.tv_usec);
        if (timeoutval <= 0)
        {
            ereport(LOG,
                    (errmsg("timeout waiting for RADIUS response from %s",
                            server)));
            closesocket(sock);
            return STATUS_ERROR;
        }
        timeout.tv_sec = timeoutval / 1000000;
        timeout.tv_usec = timeoutval % 1000000;

        FD_ZERO(&fdset);
        FD_SET(sock, &fdset);

        r = select(sock + 1, &fdset, NULL, NULL, &timeout);
        if (r < 0)
        {
            if (errno == EINTR)
                continue;

            /* Anything else is an actual error */
            ereport(LOG,
                    (errmsg("could not check status on RADIUS socket: %m")));
            closesocket(sock);
            return STATUS_ERROR;
        }
        if (r == 0)
        {
            ereport(LOG,
                    (errmsg("timeout waiting for RADIUS response from %s",
                            server)));
            closesocket(sock);
            return STATUS_ERROR;
        }

        /*
         * Attempt to read the response packet, and verify the contents.
         *
         * Any packet that's not actually a RADIUS packet, or otherwise does
         * not validate as an explicit reject, is just ignored and we retry
         * for another packet (until we reach the timeout). This is to avoid
         * the possibility to denial-of-service the login by flooding the
         * server with invalid packets on the port that we're expecting the
         * RADIUS response on.
         */

        addrsize = sizeof(remoteaddr);
        packetlength = recvfrom(sock, receive_buffer, RADIUS_BUFFER_SIZE, 0,
                                (struct sockaddr *) &remoteaddr, &addrsize);
        if (packetlength < 0)
        {
            ereport(LOG,
                    (errmsg("could not read RADIUS response: %m")));
            closesocket(sock);
            return STATUS_ERROR;
        }

#ifdef HAVE_IPV6
        if (remoteaddr.sin6_port != pg_hton16(port))
#else
        if (remoteaddr.sin_port != pg_hton16(port))
#endif
        {
#ifdef HAVE_IPV6
            ereport(LOG,
                    (errmsg("RADIUS response from %s was sent from incorrect port: %d",
                            server, pg_ntoh16(remoteaddr.sin6_port))));
#else
            ereport(LOG,
                    (errmsg("RADIUS response from %s was sent from incorrect port: %d",
                            server, pg_ntoh16(remoteaddr.sin_port))));
#endif
            continue;
        }

        if (packetlength < RADIUS_HEADER_LENGTH)
        {
            ereport(LOG,
                    (errmsg("RADIUS response from %s too short: %d", server, packetlength)));
            continue;
        }

        if (packetlength != pg_ntoh16(receivepacket->length))
        {
            ereport(LOG,
                    (errmsg("RADIUS response from %s has corrupt length: %d (actual length %d)",
                            server, pg_ntoh16(receivepacket->length), packetlength)));
            continue;
        }

        if (packet->id != receivepacket->id)
        {
            ereport(LOG,
                    (errmsg("RADIUS response from %s is to a different request: %d (should be %d)",
                            server, receivepacket->id, packet->id)));
            continue;
        }

        /*
         * Verify the response authenticator, which is calculated as
         * MD5(Code+ID+Length+RequestAuthenticator+Attributes+Secret)
         */
        cryptvector = palloc(packetlength + strlen(secret));

        memcpy(cryptvector, receivepacket, 4);  /* code+id+length */
        memcpy(cryptvector + 4, packet->vector, RADIUS_VECTOR_LENGTH);  /* request
                                                                         * authenticator, from
                                                                         * original packet */
        if (packetlength > RADIUS_HEADER_LENGTH)    /* there may be no
                                                     * attributes at all */
            memcpy(cryptvector + RADIUS_HEADER_LENGTH, receive_buffer + RADIUS_HEADER_LENGTH, packetlength - RADIUS_HEADER_LENGTH);
        memcpy(cryptvector + packetlength, secret, strlen(secret));

        if (!pg_md5_binary(cryptvector,
                           packetlength + strlen(secret),
                           encryptedpassword))
        {
            ereport(LOG,
                    (errmsg("could not perform MD5 encryption of received packet")));
            pfree(cryptvector);
            continue;
        }
        pfree(cryptvector);

        if (memcmp(receivepacket->vector, encryptedpassword, RADIUS_VECTOR_LENGTH) != 0)
        {
            ereport(LOG,
                    (errmsg("RADIUS response from %s has incorrect MD5 signature",
                            server)));
            continue;
        }

        if (receivepacket->code == RADIUS_ACCESS_ACCEPT)
        {
            closesocket(sock);
            return STATUS_OK;
        }
        else if (receivepacket->code == RADIUS_ACCESS_REJECT)
        {
            closesocket(sock);
            return STATUS_EOF;
        }
        else
        {
            ereport(LOG,
                    (errmsg("RADIUS response from %s has invalid code (%d) for user \"%s\"",
                            server, receivepacket->code, user_name)));
            continue;
        }
    }                           /* while (true) */
}