fe-auth.c

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/*-------------------------------------------------------------------------
 *
 * fe-auth.c
 *     The front-end (client) authorization routines
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/interfaces/libpq/fe-auth.c
 *
 *-------------------------------------------------------------------------
 */

/*
 * INTERFACE ROUTINES
 *     frontend (client) routines:
 *      pg_fe_sendauth          send authentication information
 *      pg_fe_getauthname       get user's name according to the client side
 *                              of the authentication system
 */

#include "postgres_fe.h"

#ifdef WIN32
#include "win32.h"
#else
#include <unistd.h>
#include <fcntl.h>
#include <sys/param.h>          /* for MAXHOSTNAMELEN on most */
#include <sys/socket.h>
#ifdef HAVE_SYS_UCRED_H
#include <sys/ucred.h>
#endif
#ifndef  MAXHOSTNAMELEN
#include <netdb.h>              /* for MAXHOSTNAMELEN on some */
#endif
#include <pwd.h>
#endif

#include "common/md5.h"
#include "common/scram-common.h"
#include "fe-auth.h"
#include "libpq-fe.h"

#ifdef ENABLE_GSS
/*
 * GSSAPI authentication system.
 */

#include "fe-gssapi-common.h"

/*
 * Continue GSS authentication with next token as needed.
 */
static int
pg_GSS_continue(PGconn *conn, int payloadlen)
{
    OM_uint32   maj_stat,
                min_stat,
                lmin_s;
    gss_buffer_desc ginbuf;
    gss_buffer_desc goutbuf;

    /*
     * On first call, there's no input token. On subsequent calls, read the
     * input token into a GSS buffer.
     */
    if (conn->gctx != GSS_C_NO_CONTEXT)
    {
        ginbuf.length = payloadlen;
        ginbuf.value = malloc(payloadlen);
        if (!ginbuf.value)
        {
            appendPQExpBuffer(&conn->errorMessage,
                              libpq_gettext("out of memory allocating GSSAPI buffer (%d)\n"),
                              payloadlen);
            return STATUS_ERROR;
        }
        if (pqGetnchar(ginbuf.value, payloadlen, conn))
        {
            /*
             * Shouldn't happen, because the caller should've ensured that the
             * whole message is already in the input buffer.
             */
            free(ginbuf.value);
            return STATUS_ERROR;
        }
    }
    else
    {
        ginbuf.length = 0;
        ginbuf.value = NULL;
    }

    maj_stat = gss_init_sec_context(&min_stat,
                                    GSS_C_NO_CREDENTIAL,
                                    &conn->gctx,
                                    conn->gtarg_nam,
                                    GSS_C_NO_OID,
                                    GSS_C_MUTUAL_FLAG,
                                    0,
                                    GSS_C_NO_CHANNEL_BINDINGS,
                                    (ginbuf.value == NULL) ? GSS_C_NO_BUFFER : &ginbuf,
                                    NULL,
                                    &goutbuf,
                                    NULL,
                                    NULL);

    if (ginbuf.value)
        free(ginbuf.value);

    if (goutbuf.length != 0)
    {
        /*
         * GSS generated data to send to the server. We don't care if it's the
         * first or subsequent packet, just send the same kind of password
         * packet.
         */
        if (pqPacketSend(conn, 'p',
                         goutbuf.value, goutbuf.length) != STATUS_OK)
        {
            gss_release_buffer(&lmin_s, &goutbuf);
            return STATUS_ERROR;
        }
    }
    gss_release_buffer(&lmin_s, &goutbuf);

    if (maj_stat != GSS_S_COMPLETE && maj_stat != GSS_S_CONTINUE_NEEDED)
    {
        pg_GSS_error(libpq_gettext("GSSAPI continuation error"),
                     conn,
                     maj_stat, min_stat);
        gss_release_name(&lmin_s, &conn->gtarg_nam);
        if (conn->gctx)
            gss_delete_sec_context(&lmin_s, &conn->gctx, GSS_C_NO_BUFFER);
        return STATUS_ERROR;
    }

    if (maj_stat == GSS_S_COMPLETE)
        gss_release_name(&lmin_s, &conn->gtarg_nam);

    return STATUS_OK;
}

/*
 * Send initial GSS authentication token
 */
static int
pg_GSS_startup(PGconn *conn, int payloadlen)
{
    int         ret;
    char       *host = conn->connhost[conn->whichhost].host;

    if (!(host && host[0] != '\0'))
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("host name must be specified\n"));
        return STATUS_ERROR;
    }

    if (conn->gctx)
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("duplicate GSS authentication request\n"));
        return STATUS_ERROR;
    }

    ret = pg_GSS_load_servicename(conn);
    if (ret != STATUS_OK)
        return ret;

    /*
     * Initial packet is the same as a continuation packet with no initial
     * context.
     */
    conn->gctx = GSS_C_NO_CONTEXT;

    return pg_GSS_continue(conn, payloadlen);
}
#endif                          /* ENABLE_GSS */


#ifdef ENABLE_SSPI
/*
 * SSPI authentication system (Windows only)
 */

static void
pg_SSPI_error(PGconn *conn, const char *mprefix, SECURITY_STATUS r)
{
    char        sysmsg[256];

    if (FormatMessage(FORMAT_MESSAGE_IGNORE_INSERTS |
                      FORMAT_MESSAGE_FROM_SYSTEM,
                      NULL, r, 0,
                      sysmsg, sizeof(sysmsg), NULL) == 0)
        appendPQExpBuffer(&conn->errorMessage, "%s: SSPI error %x\n",
                          mprefix, (unsigned int) r);
    else
        appendPQExpBuffer(&conn->errorMessage, "%s: %s (%x)\n",
                          mprefix, sysmsg, (unsigned int) r);
}

/*
 * Continue SSPI authentication with next token as needed.
 */
static int
pg_SSPI_continue(PGconn *conn, int payloadlen)
{
    SECURITY_STATUS r;
    CtxtHandle  newContext;
    ULONG       contextAttr;
    SecBufferDesc inbuf;
    SecBufferDesc outbuf;
    SecBuffer   OutBuffers[1];
    SecBuffer   InBuffers[1];
    char       *inputbuf = NULL;

    if (conn->sspictx != NULL)
    {
        /*
         * On runs other than the first we have some data to send. Put this
         * data in a SecBuffer type structure.
         */
        inputbuf = malloc(payloadlen);
        if (!inputbuf)
        {
            appendPQExpBuffer(&conn->errorMessage,
                              libpq_gettext("out of memory allocating SSPI buffer (%d)\n"),
                              payloadlen);
            return STATUS_ERROR;
        }
        if (pqGetnchar(inputbuf, payloadlen, conn))
        {
            /*
             * Shouldn't happen, because the caller should've ensured that the
             * whole message is already in the input buffer.
             */
            free(inputbuf);
            return STATUS_ERROR;
        }

        inbuf.ulVersion = SECBUFFER_VERSION;
        inbuf.cBuffers = 1;
        inbuf.pBuffers = InBuffers;
        InBuffers[0].pvBuffer = inputbuf;
        InBuffers[0].cbBuffer = payloadlen;
        InBuffers[0].BufferType = SECBUFFER_TOKEN;
    }

    OutBuffers[0].pvBuffer = NULL;
    OutBuffers[0].BufferType = SECBUFFER_TOKEN;
    OutBuffers[0].cbBuffer = 0;
    outbuf.cBuffers = 1;
    outbuf.pBuffers = OutBuffers;
    outbuf.ulVersion = SECBUFFER_VERSION;

    r = InitializeSecurityContext(conn->sspicred,
                                  conn->sspictx,
                                  conn->sspitarget,
                                  ISC_REQ_ALLOCATE_MEMORY,
                                  0,
                                  SECURITY_NETWORK_DREP,
                                  (conn->sspictx == NULL) ? NULL : &inbuf,
                                  0,
                                  &newContext,
                                  &outbuf,
                                  &contextAttr,
                                  NULL);

    /* we don't need the input anymore */
    if (inputbuf)
        free(inputbuf);

    if (r != SEC_E_OK && r != SEC_I_CONTINUE_NEEDED)
    {
        pg_SSPI_error(conn, libpq_gettext("SSPI continuation error"), r);

        return STATUS_ERROR;
    }

    if (conn->sspictx == NULL)
    {
        /* On first run, transfer retrieved context handle */
        conn->sspictx = malloc(sizeof(CtxtHandle));
        if (conn->sspictx == NULL)
        {
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("out of memory\n"));
            return STATUS_ERROR;
        }
        memcpy(conn->sspictx, &newContext, sizeof(CtxtHandle));
    }

    /*
     * If SSPI returned any data to be sent to the server (as it normally
     * would), send this data as a password packet.
     */
    if (outbuf.cBuffers > 0)
    {
        if (outbuf.cBuffers != 1)
        {
            /*
             * This should never happen, at least not for Kerberos
             * authentication. Keep check in case it shows up with other
             * authentication methods later.
             */
            appendPQExpBufferStr(&conn->errorMessage,
                                 "SSPI returned invalid number of output buffers\n");
            return STATUS_ERROR;
        }

        /*
         * If the negotiation is complete, there may be zero bytes to send.
         * The server is at this point not expecting any more data, so don't
         * send it.
         */
        if (outbuf.pBuffers[0].cbBuffer > 0)
        {
            if (pqPacketSend(conn, 'p',
                             outbuf.pBuffers[0].pvBuffer, outbuf.pBuffers[0].cbBuffer))
            {
                FreeContextBuffer(outbuf.pBuffers[0].pvBuffer);
                return STATUS_ERROR;
            }
        }
        FreeContextBuffer(outbuf.pBuffers[0].pvBuffer);
    }

    /* Cleanup is handled by the code in freePGconn() */
    return STATUS_OK;
}

/*
 * Send initial SSPI authentication token.
 * If use_negotiate is 0, use kerberos authentication package which is
 * compatible with Unix. If use_negotiate is 1, use the negotiate package
 * which supports both kerberos and NTLM, but is not compatible with Unix.
 */
static int
pg_SSPI_startup(PGconn *conn, int use_negotiate, int payloadlen)
{
    SECURITY_STATUS r;
    TimeStamp   expire;
    char       *host = conn->connhost[conn->whichhost].host;

    if (conn->sspictx)
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("duplicate SSPI authentication request\n"));
        return STATUS_ERROR;
    }

    /*
     * Retrieve credentials handle
     */
    conn->sspicred = malloc(sizeof(CredHandle));
    if (conn->sspicred == NULL)
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("out of memory\n"));
        return STATUS_ERROR;
    }

    r = AcquireCredentialsHandle(NULL,
                                 use_negotiate ? "negotiate" : "kerberos",
                                 SECPKG_CRED_OUTBOUND,
                                 NULL,
                                 NULL,
                                 NULL,
                                 NULL,
                                 conn->sspicred,
                                 &expire);
    if (r != SEC_E_OK)
    {
        pg_SSPI_error(conn, libpq_gettext("could not acquire SSPI credentials"), r);
        free(conn->sspicred);
        conn->sspicred = NULL;
        return STATUS_ERROR;
    }

    /*
     * Compute target principal name. SSPI has a different format from GSSAPI,
     * but not more complex. We can skip the @REALM part, because Windows will
     * fill that in for us automatically.
     */
    if (!(host && host[0] != '\0'))
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("host name must be specified\n"));
        return STATUS_ERROR;
    }
    conn->sspitarget = malloc(strlen(conn->krbsrvname) + strlen(host) + 2);
    if (!conn->sspitarget)
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("out of memory\n"));
        return STATUS_ERROR;
    }
    sprintf(conn->sspitarget, "%s/%s", conn->krbsrvname, host);

    /*
     * Indicate that we're in SSPI authentication mode to make sure that
     * pg_SSPI_continue is called next time in the negotiation.
     */
    conn->usesspi = 1;

    return pg_SSPI_continue(conn, payloadlen);
}
#endif                          /* ENABLE_SSPI */

/*
 * Initialize SASL authentication exchange.
 */
static int
pg_SASL_init(PGconn *conn, int payloadlen)
{
    char       *initialresponse = NULL;
    int         initialresponselen;
    bool        done;
    bool        success;
    const char *selected_mechanism;
    PQExpBufferData mechanism_buf;
    char       *password;

    initPQExpBuffer(&mechanism_buf);

    if (conn->channel_binding[0] == 'r' &&  /* require */
        !conn->ssl_in_use)
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("channel binding required, but SSL not in use\n"));
        goto error;
    }

    if (conn->sasl_state)
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("duplicate SASL authentication request\n"));
        goto error;
    }

    /*
     * Parse the list of SASL authentication mechanisms in the
     * AuthenticationSASL message, and select the best mechanism that we
     * support.  SCRAM-SHA-256-PLUS and SCRAM-SHA-256 are the only ones
     * supported at the moment, listed by order of decreasing importance.
     */
    selected_mechanism = NULL;
    for (;;)
    {
        if (pqGets(&mechanism_buf, conn))
        {
            appendPQExpBufferStr(&conn->errorMessage,
                                 "fe_sendauth: invalid authentication request from server: invalid list of authentication mechanisms\n");
            goto error;
        }
        if (PQExpBufferDataBroken(mechanism_buf))
            goto oom_error;

        /* An empty string indicates end of list */
        if (mechanism_buf.data[0] == '\0')
            break;

        /*
         * Select the mechanism to use.  Pick SCRAM-SHA-256-PLUS over anything
         * else if a channel binding type is set and if the client supports it
         * (and did not set channel_binding=disable). Pick SCRAM-SHA-256 if
         * nothing else has already been picked.  If we add more mechanisms, a
         * more refined priority mechanism might become necessary.
         */
        if (strcmp(mechanism_buf.data, SCRAM_SHA_256_PLUS_NAME) == 0)
        {
            if (conn->ssl_in_use)
            {
                /* The server has offered SCRAM-SHA-256-PLUS. */

#ifdef HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH
                /*
                 * The client supports channel binding, which is chosen if
                 * channel_binding is not disabled.
                 */
                if (conn->channel_binding[0] != 'd')    /* disable */
                    selected_mechanism = SCRAM_SHA_256_PLUS_NAME;
#else
                /*
                 * The client does not support channel binding.  If it is
                 * required, complain immediately instead of the error below
                 * which would be confusing as the server is publishing
                 * SCRAM-SHA-256-PLUS.
                 */
                if (conn->channel_binding[0] == 'r')    /* require */
                {
                    appendPQExpBufferStr(&conn->errorMessage,
                                         libpq_gettext("channel binding is required, but client does not support it\n"));
                    goto error;
                }
#endif
            }
            else
            {
                /*
                 * The server offered SCRAM-SHA-256-PLUS, but the connection
                 * is not SSL-encrypted. That's not sane. Perhaps SSL was
                 * stripped by a proxy? There's no point in continuing,
                 * because the server will reject the connection anyway if we
                 * try authenticate without channel binding even though both
                 * the client and server supported it. The SCRAM exchange
                 * checks for that, to prevent downgrade attacks.
                 */
                appendPQExpBufferStr(&conn->errorMessage,
                                     libpq_gettext("server offered SCRAM-SHA-256-PLUS authentication over a non-SSL connection\n"));
                goto error;
            }
        }
        else if (strcmp(mechanism_buf.data, SCRAM_SHA_256_NAME) == 0 &&
                 !selected_mechanism)
            selected_mechanism = SCRAM_SHA_256_NAME;
    }

    if (!selected_mechanism)
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("none of the server's SASL authentication mechanisms are supported\n"));
        goto error;
    }

    if (conn->channel_binding[0] == 'r' &&  /* require */
        strcmp(selected_mechanism, SCRAM_SHA_256_PLUS_NAME) != 0)
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("channel binding is required, but server did not offer an authentication method that supports channel binding\n"));
        goto error;
    }

    /*
     * Now that the SASL mechanism has been chosen for the exchange,
     * initialize its state information.
     */

    /*
     * First, select the password to use for the exchange, complaining if
     * there isn't one.  Currently, all supported SASL mechanisms require a
     * password, so we can just go ahead here without further distinction.
     */
    conn->password_needed = true;
    password = conn->connhost[conn->whichhost].password;
    if (password == NULL)
        password = conn->pgpass;
    if (password == NULL || password[0] == '\0')
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             PQnoPasswordSupplied);
        goto error;
    }

    /*
     * Initialize the SASL state information with all the information gathered
     * during the initial exchange.
     *
     * Note: Only tls-unique is supported for the moment.
     */
    conn->sasl_state = pg_fe_scram_init(conn,
                                        password,
                                        selected_mechanism);
    if (!conn->sasl_state)
        goto oom_error;

    /* Get the mechanism-specific Initial Client Response, if any */
    pg_fe_scram_exchange(conn->sasl_state,
                         NULL, -1,
                         &initialresponse, &initialresponselen,
                         &done, &success);

    if (done && !success)
        goto error;

    /*
     * Build a SASLInitialResponse message, and send it.
     */
    if (pqPutMsgStart('p', conn))
        goto error;
    if (pqPuts(selected_mechanism, conn))
        goto error;
    if (initialresponse)
    {
        if (pqPutInt(initialresponselen, 4, conn))
            goto error;
        if (pqPutnchar(initialresponse, initialresponselen, conn))
            goto error;
    }
    if (pqPutMsgEnd(conn))
        goto error;
    if (pqFlush(conn))
        goto error;

    termPQExpBuffer(&mechanism_buf);
    if (initialresponse)
        free(initialresponse);

    return STATUS_OK;

error:
    termPQExpBuffer(&mechanism_buf);
    if (initialresponse)
        free(initialresponse);
    return STATUS_ERROR;

oom_error:
    termPQExpBuffer(&mechanism_buf);
    if (initialresponse)
        free(initialresponse);
    appendPQExpBufferStr(&conn->errorMessage,
                         libpq_gettext("out of memory\n"));
    return STATUS_ERROR;
}

/*
 * Exchange a message for SASL communication protocol with the backend.
 * This should be used after calling pg_SASL_init to set up the status of
 * the protocol.
 */
static int
pg_SASL_continue(PGconn *conn, int payloadlen, bool final)
{
    char       *output;
    int         outputlen;
    bool        done;
    bool        success;
    int         res;
    char       *challenge;

    /* Read the SASL challenge from the AuthenticationSASLContinue message. */
    challenge = malloc(payloadlen + 1);
    if (!challenge)
    {
        appendPQExpBuffer(&conn->errorMessage,
                          libpq_gettext("out of memory allocating SASL buffer (%d)\n"),
                          payloadlen);
        return STATUS_ERROR;
    }

    if (pqGetnchar(challenge, payloadlen, conn))
    {
        free(challenge);
        return STATUS_ERROR;
    }
    /* For safety and convenience, ensure the buffer is NULL-terminated. */
    challenge[payloadlen] = '\0';

    pg_fe_scram_exchange(conn->sasl_state,
                         challenge, payloadlen,
                         &output, &outputlen,
                         &done, &success);
    free(challenge);            /* don't need the input anymore */

    if (final && !done)
    {
        if (outputlen != 0)
            free(output);

        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("AuthenticationSASLFinal received from server, but SASL authentication was not completed\n"));
        return STATUS_ERROR;
    }
    if (outputlen != 0)
    {
        /*
         * Send the SASL response to the server.
         */
        res = pqPacketSend(conn, 'p', output, outputlen);
        free(output);

        if (res != STATUS_OK)
            return STATUS_ERROR;
    }

    if (done && !success)
        return STATUS_ERROR;

    return STATUS_OK;
}

/*
 * Respond to AUTH_REQ_SCM_CREDS challenge.
 *
 * Note: this is dead code as of Postgres 9.1, because current backends will
 * never send this challenge.  But we must keep it as long as libpq needs to
 * interoperate with pre-9.1 servers.  It is believed to be needed only on
 * Debian/kFreeBSD (ie, FreeBSD kernel with Linux userland, so that the
 * getpeereid() function isn't provided by libc).
 */
static int
pg_local_sendauth(PGconn *conn)
{
#ifdef HAVE_STRUCT_CMSGCRED
    char        buf;
    struct iovec iov;
    struct msghdr msg;
    struct cmsghdr *cmsg;
    union
    {
        struct cmsghdr hdr;
        unsigned char buf[CMSG_SPACE(sizeof(struct cmsgcred))];
    }           cmsgbuf;

    /*
     * The backend doesn't care what we send here, but it wants exactly one
     * character to force recvmsg() to block and wait for us.
     */
    buf = '\0';
    iov.iov_base = &buf;
    iov.iov_len = 1;

    memset(&msg, 0, sizeof(msg));
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;

    /* We must set up a message that will be filled in by kernel */
    memset(&cmsgbuf, 0, sizeof(cmsgbuf));
    msg.msg_control = &cmsgbuf.buf;
    msg.msg_controllen = sizeof(cmsgbuf.buf);
    cmsg = CMSG_FIRSTHDR(&msg);
    cmsg->cmsg_len = CMSG_LEN(sizeof(struct cmsgcred));
    cmsg->cmsg_level = SOL_SOCKET;
    cmsg->cmsg_type = SCM_CREDS;

    if (sendmsg(conn->sock, &msg, 0) == -1)
    {
        char        sebuf[PG_STRERROR_R_BUFLEN];

        appendPQExpBuffer(&conn->errorMessage,
                          "pg_local_sendauth: sendmsg: %s\n",
                          strerror_r(errno, sebuf, sizeof(sebuf)));
        return STATUS_ERROR;
    }
    return STATUS_OK;
#else
    appendPQExpBufferStr(&conn->errorMessage,
                         libpq_gettext("SCM_CRED authentication method not supported\n"));
    return STATUS_ERROR;
#endif
}

static int
pg_password_sendauth(PGconn *conn, const char *password, AuthRequest areq)
{
    int         ret;
    char       *crypt_pwd = NULL;
    const char *pwd_to_send;
    char        md5Salt[4];

    /* Read the salt from the AuthenticationMD5Password message. */
    if (areq == AUTH_REQ_MD5)
    {
        if (pqGetnchar(md5Salt, 4, conn))
            return STATUS_ERROR;    /* shouldn't happen */
    }

    /* Encrypt the password if needed. */

    switch (areq)
    {
        case AUTH_REQ_MD5:
            {
                char       *crypt_pwd2;

                /* Allocate enough space for two MD5 hashes */
                crypt_pwd = malloc(2 * (MD5_PASSWD_LEN + 1));
                if (!crypt_pwd)
                {
                    appendPQExpBufferStr(&conn->errorMessage,
                                         libpq_gettext("out of memory\n"));
                    return STATUS_ERROR;
                }

                crypt_pwd2 = crypt_pwd + MD5_PASSWD_LEN + 1;
                if (!pg_md5_encrypt(password, conn->pguser,
                                    strlen(conn->pguser), crypt_pwd2))
                {
                    free(crypt_pwd);
                    return STATUS_ERROR;
                }
                if (!pg_md5_encrypt(crypt_pwd2 + strlen("md5"), md5Salt,
                                    4, crypt_pwd))
                {
                    free(crypt_pwd);
                    return STATUS_ERROR;
                }

                pwd_to_send = crypt_pwd;
                break;
            }
        case AUTH_REQ_PASSWORD:
            pwd_to_send = password;
            break;
        default:
            return STATUS_ERROR;
    }
    ret = pqPacketSend(conn, 'p', pwd_to_send, strlen(pwd_to_send) + 1);
    if (crypt_pwd)
        free(crypt_pwd);
    return ret;
}

/*
 * Verify that the authentication request is expected, given the connection
 * parameters. This is especially important when the client wishes to
 * authenticate the server before any sensitive information is exchanged.
 */
static bool
check_expected_areq(AuthRequest areq, PGconn *conn)
{
    bool        result = true;

    /*
     * When channel_binding=require, we must protect against two cases: (1) we
     * must not respond to non-SASL authentication requests, which might leak
     * information such as the client's password; and (2) even if we receive
     * AUTH_REQ_OK, we still must ensure that channel binding has happened in
     * order to authenticate the server.
     */
    if (conn->channel_binding[0] == 'r' /* require */ )
    {
        switch (areq)
        {
            case AUTH_REQ_SASL:
            case AUTH_REQ_SASL_CONT:
            case AUTH_REQ_SASL_FIN:
                break;
            case AUTH_REQ_OK:
                if (!pg_fe_scram_channel_bound(conn->sasl_state))
                {
                    appendPQExpBufferStr(&conn->errorMessage,
                                         libpq_gettext("channel binding required, but server authenticated client without channel binding\n"));
                    result = false;
                }
                break;
            default:
                appendPQExpBufferStr(&conn->errorMessage,
                                     libpq_gettext("channel binding required but not supported by server's authentication request\n"));
                result = false;
                break;
        }
    }

    return result;
}

/*
 * pg_fe_sendauth
 *      client demux routine for processing an authentication request
 *
 * The server has sent us an authentication challenge (or OK). Send an
 * appropriate response. The caller has ensured that the whole message is
 * now in the input buffer, and has already read the type and length of
 * it. We are responsible for reading any remaining extra data, specific
 * to the authentication method. 'payloadlen' is the remaining length in
 * the message.
 */
int
pg_fe_sendauth(AuthRequest areq, int payloadlen, PGconn *conn)
{
    int         oldmsglen;

    if (!check_expected_areq(areq, conn))
        return STATUS_ERROR;

    switch (areq)
    {
        case AUTH_REQ_OK:
            break;

        case AUTH_REQ_KRB4:
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("Kerberos 4 authentication not supported\n"));
            return STATUS_ERROR;

        case AUTH_REQ_KRB5:
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("Kerberos 5 authentication not supported\n"));
            return STATUS_ERROR;

#if defined(ENABLE_GSS) || defined(ENABLE_SSPI)
        case AUTH_REQ_GSS:
#if !defined(ENABLE_SSPI)
            /* no native SSPI, so use GSSAPI library for it */
        case AUTH_REQ_SSPI:
#endif
            {
                int         r;

                pglock_thread();

                /*
                 * If we have both GSS and SSPI support compiled in, use SSPI
                 * support by default. This is overridable by a connection
                 * string parameter. Note that when using SSPI we still leave
                 * the negotiate parameter off, since we want SSPI to use the
                 * GSSAPI kerberos protocol. For actual SSPI negotiate
                 * protocol, we use AUTH_REQ_SSPI.
                 */
#if defined(ENABLE_GSS) && defined(ENABLE_SSPI)
                if (conn->gsslib && (pg_strcasecmp(conn->gsslib, "gssapi") == 0))
                    r = pg_GSS_startup(conn, payloadlen);
                else
                    r = pg_SSPI_startup(conn, 0, payloadlen);
#elif defined(ENABLE_GSS) && !defined(ENABLE_SSPI)
                r = pg_GSS_startup(conn, payloadlen);
#elif !defined(ENABLE_GSS) && defined(ENABLE_SSPI)
                r = pg_SSPI_startup(conn, 0, payloadlen);
#endif
                if (r != STATUS_OK)
                {
                    /* Error message already filled in. */
                    pgunlock_thread();
                    return STATUS_ERROR;
                }
                pgunlock_thread();
            }
            break;

        case AUTH_REQ_GSS_CONT:
            {
                int         r;

                pglock_thread();
#if defined(ENABLE_GSS) && defined(ENABLE_SSPI)
                if (conn->usesspi)
                    r = pg_SSPI_continue(conn, payloadlen);
                else
                    r = pg_GSS_continue(conn, payloadlen);
#elif defined(ENABLE_GSS) && !defined(ENABLE_SSPI)
                r = pg_GSS_continue(conn, payloadlen);
#elif !defined(ENABLE_GSS) && defined(ENABLE_SSPI)
                r = pg_SSPI_continue(conn, payloadlen);
#endif
                if (r != STATUS_OK)
                {
                    /* Error message already filled in. */
                    pgunlock_thread();
                    return STATUS_ERROR;
                }
                pgunlock_thread();
            }
            break;
#else                           /* defined(ENABLE_GSS) || defined(ENABLE_SSPI) */
            /* No GSSAPI *or* SSPI support */
        case AUTH_REQ_GSS:
        case AUTH_REQ_GSS_CONT:
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("GSSAPI authentication not supported\n"));
            return STATUS_ERROR;
#endif                          /* defined(ENABLE_GSS) || defined(ENABLE_SSPI) */

#ifdef ENABLE_SSPI
        case AUTH_REQ_SSPI:

            /*
             * SSPI has its own startup message so libpq can decide which
             * method to use. Indicate to pg_SSPI_startup that we want SSPI
             * negotiation instead of Kerberos.
             */
            pglock_thread();
            if (pg_SSPI_startup(conn, 1, payloadlen) != STATUS_OK)
            {
                /* Error message already filled in. */
                pgunlock_thread();
                return STATUS_ERROR;
            }
            pgunlock_thread();
            break;
#else

            /*
             * No SSPI support. However, if we have GSSAPI but not SSPI
             * support, AUTH_REQ_SSPI will have been handled in the codepath
             * for AUTH_REQ_GSS above, so don't duplicate the case label in
             * that case.
             */
#if !defined(ENABLE_GSS)
        case AUTH_REQ_SSPI:
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("SSPI authentication not supported\n"));
            return STATUS_ERROR;
#endif                          /* !define(ENABLE_GSS) */
#endif                          /* ENABLE_SSPI */


        case AUTH_REQ_CRYPT:
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("Crypt authentication not supported\n"));
            return STATUS_ERROR;

        case AUTH_REQ_MD5:
        case AUTH_REQ_PASSWORD:
            {
                char       *password;

                conn->password_needed = true;
                password = conn->connhost[conn->whichhost].password;
                if (password == NULL)
                    password = conn->pgpass;
                if (password == NULL || password[0] == '\0')
                {
                    appendPQExpBufferStr(&conn->errorMessage,
                                         PQnoPasswordSupplied);
                    return STATUS_ERROR;
                }
                if (pg_password_sendauth(conn, password, areq) != STATUS_OK)
                {
                    appendPQExpBufferStr(&conn->errorMessage,
                                         "fe_sendauth: error sending password authentication\n");
                    return STATUS_ERROR;
                }
                break;
            }

        case AUTH_REQ_SASL:

            /*
             * The request contains the name (as assigned by IANA) of the
             * authentication mechanism.
             */
            if (pg_SASL_init(conn, payloadlen) != STATUS_OK)
            {
                /* pg_SASL_init already set the error message */
                return STATUS_ERROR;
            }
            break;

        case AUTH_REQ_SASL_CONT:
        case AUTH_REQ_SASL_FIN:
            if (conn->sasl_state == NULL)
            {
                appendPQExpBufferStr(&conn->errorMessage,
                                     "fe_sendauth: invalid authentication request from server: AUTH_REQ_SASL_CONT without AUTH_REQ_SASL\n");
                return STATUS_ERROR;
            }
            oldmsglen = conn->errorMessage.len;
            if (pg_SASL_continue(conn, payloadlen,
                                 (areq == AUTH_REQ_SASL_FIN)) != STATUS_OK)
            {
                /* Use this message if pg_SASL_continue didn't supply one */
                if (conn->errorMessage.len == oldmsglen)
                    appendPQExpBufferStr(&conn->errorMessage,
                                         "fe_sendauth: error in SASL authentication\n");
                return STATUS_ERROR;
            }
            break;

        case AUTH_REQ_SCM_CREDS:
            if (pg_local_sendauth(conn) != STATUS_OK)
                return STATUS_ERROR;
            break;

        default:
            appendPQExpBuffer(&conn->errorMessage,
                              libpq_gettext("authentication method %u not supported\n"), areq);
            return STATUS_ERROR;
    }

    return STATUS_OK;
}


/*
 * pg_fe_getauthname
 *
 * Returns a pointer to malloc'd space containing whatever name the user
 * has authenticated to the system.  If there is an error, return NULL,
 * and append a suitable error message to *errorMessage if that's not NULL.
 */
char *
pg_fe_getauthname(PQExpBuffer errorMessage)
{
    char       *result = NULL;
    const char *name = NULL;

#ifdef WIN32
    /* Microsoft recommends buffer size of UNLEN+1, where UNLEN = 256 */
    char        username[256 + 1];
    DWORD       namesize = sizeof(username);
#else
    uid_t       user_id = geteuid();
    char        pwdbuf[BUFSIZ];
    struct passwd pwdstr;
    struct passwd *pw = NULL;
    int         pwerr;
#endif

    /*
     * Some users are using configure --enable-thread-safety-force, so we
     * might as well do the locking within our library to protect
     * pqGetpwuid(). In fact, application developers can use getpwuid() in
     * their application if they use the locking call we provide, or install
     * their own locking function using PQregisterThreadLock().
     */
    pglock_thread();

#ifdef WIN32
    if (GetUserName(username, &namesize))
        name = username;
    else if (errorMessage)
        appendPQExpBuffer(errorMessage,
                          libpq_gettext("user name lookup failure: error code %lu\n"),
                          GetLastError());
#else
    pwerr = pqGetpwuid(user_id, &pwdstr, pwdbuf, sizeof(pwdbuf), &pw);
    if (pw != NULL)
        name = pw->pw_name;
    else if (errorMessage)
    {
        if (pwerr != 0)
            appendPQExpBuffer(errorMessage,
                              libpq_gettext("could not look up local user ID %d: %s\n"),
                              (int) user_id,
                              strerror_r(pwerr, pwdbuf, sizeof(pwdbuf)));
        else
            appendPQExpBuffer(errorMessage,
                              libpq_gettext("local user with ID %d does not exist\n"),
                              (int) user_id);
    }
#endif

    if (name)
    {
        result = strdup(name);
        if (result == NULL && errorMessage)
            appendPQExpBufferStr(errorMessage,
                                 libpq_gettext("out of memory\n"));
    }

    pgunlock_thread();

    return result;
}


/*
 * PQencryptPassword -- exported routine to encrypt a password with MD5
 *
 * This function is equivalent to calling PQencryptPasswordConn with
 * "md5" as the encryption method, except that this doesn't require
 * a connection object.  This function is deprecated, use
 * PQencryptPasswordConn instead.
 */
char *
PQencryptPassword(const char *passwd, const char *user)
{
    char       *crypt_pwd;

    crypt_pwd = malloc(MD5_PASSWD_LEN + 1);
    if (!crypt_pwd)
        return NULL;

    if (!pg_md5_encrypt(passwd, user, strlen(user), crypt_pwd))
    {
        free(crypt_pwd);
        return NULL;
    }

    return crypt_pwd;
}

/*
 * PQencryptPasswordConn -- exported routine to encrypt a password
 *
 * This is intended to be used by client applications that wish to send
 * commands like ALTER USER joe PASSWORD 'pwd'.  The password need not
 * be sent in cleartext if it is encrypted on the client side.  This is
 * good because it ensures the cleartext password won't end up in logs,
 * pg_stat displays, etc.  We export the function so that clients won't
 * be dependent on low-level details like whether the encryption is MD5
 * or something else.
 *
 * Arguments are a connection object, the cleartext password, the SQL
 * name of the user it is for, and a string indicating the algorithm to
 * use for encrypting the password.  If algorithm is NULL, this queries
 * the server for the current 'password_encryption' value.  If you wish
 * to avoid that, e.g. to avoid blocking, you can execute
 * 'show password_encryption' yourself before calling this function, and
 * pass it as the algorithm.
 *
 * Return value is a malloc'd string.  The client may assume the string
 * doesn't contain any special characters that would require escaping.
 * On error, an error message is stored in the connection object, and
 * returns NULL.
 */
char *
PQencryptPasswordConn(PGconn *conn, const char *passwd, const char *user,
                      const char *algorithm)
{
#define MAX_ALGORITHM_NAME_LEN 50
    char        algobuf[MAX_ALGORITHM_NAME_LEN + 1];
    char       *crypt_pwd = NULL;

    if (!conn)
        return NULL;

    resetPQExpBuffer(&conn->errorMessage);

    /* If no algorithm was given, ask the server. */
    if (algorithm == NULL)
    {
        PGresult   *res;
        char       *val;

        res = PQexec(conn, "show password_encryption");
        if (res == NULL)
        {
            /* PQexec() should've set conn->errorMessage already */
            return NULL;
        }
        if (PQresultStatus(res) != PGRES_TUPLES_OK)
        {
            /* PQexec() should've set conn->errorMessage already */
            PQclear(res);
            return NULL;
        }
        if (PQntuples(res) != 1 || PQnfields(res) != 1)
        {
            PQclear(res);
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("unexpected shape of result set returned for SHOW\n"));
            return NULL;
        }
        val = PQgetvalue(res, 0, 0);

        if (strlen(val) > MAX_ALGORITHM_NAME_LEN)
        {
            PQclear(res);
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("password_encryption value too long\n"));
            return NULL;
        }
        strcpy(algobuf, val);
        PQclear(res);

        algorithm = algobuf;
    }

    /*
     * Also accept "on" and "off" as aliases for "md5", because
     * password_encryption was a boolean before PostgreSQL 10.  We refuse to
     * send the password in plaintext even if it was "off".
     */
    if (strcmp(algorithm, "on") == 0 ||
        strcmp(algorithm, "off") == 0)
        algorithm = "md5";

    /*
     * Ok, now we know what algorithm to use
     */
    if (strcmp(algorithm, "scram-sha-256") == 0)
    {
        crypt_pwd = pg_fe_scram_build_secret(passwd);
    }
    else if (strcmp(algorithm, "md5") == 0)
    {
        crypt_pwd = malloc(MD5_PASSWD_LEN + 1);
        if (crypt_pwd)
        {
            if (!pg_md5_encrypt(passwd, user, strlen(user), crypt_pwd))
            {
                free(crypt_pwd);
                crypt_pwd = NULL;
            }
        }
    }
    else
    {
        appendPQExpBuffer(&conn->errorMessage,
                          libpq_gettext("unrecognized password encryption algorithm \"%s\"\n"),
                          algorithm);
        return NULL;
    }

    if (!crypt_pwd)
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("out of memory\n"));

    return crypt_pwd;
}