Move routines to manipulate WAL into PostgreSQL::Test::Cluster

[pgsql.git] / src / interfaces / libpq / fe-auth.c

/*-------------------------------------------------------------------------
 *
 * fe-auth.c
 *         The front-end (client) authorization routines
 *
 * Portions Copyright (c) 1996-2025, 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 <limits.h>
#include <pwd.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
#endif

#include "common/md5.h"
#include "common/scram-common.h"
#include "fe-auth.h"
#include "fe-auth-sasl.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_flags = GSS_C_MUTUAL_FLAG;
        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)
                {
                        libpq_append_conn_error(conn, "out of memory allocating GSSAPI buffer (%d)",
                                                                        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;
        }

        /* finished parsing, trace server-to-client message */
        if (conn->Pfdebug)
                pqTraceOutputMessage(conn, conn->inBuffer + conn->inStart, false);

        /* Only try to acquire credentials if GSS delegation isn't disabled. */
        if (!pg_GSS_have_cred_cache(&conn->gcred))
                conn->gcred = GSS_C_NO_CREDENTIAL;

        if (conn->gssdelegation && conn->gssdelegation[0] == '1')
                gss_flags |= GSS_C_DELEG_FLAG;

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

        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.
                 */
                conn->current_auth_response = AUTH_RESPONSE_GSS;
                if (pqPacketSend(conn, PqMsg_GSSResponse,
                                                 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)
        {
                conn->client_finished_auth = true;
                gss_release_name(&lmin_s, &conn->gtarg_nam);
                conn->gssapi_used = true;
        }

        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'))
        {
                libpq_append_conn_error(conn, "host name must be specified");
                return STATUS_ERROR;
        }

        if (conn->gctx)
        {
                libpq_append_conn_error(conn, "duplicate GSS authentication request");
                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)
                {
                        libpq_append_conn_error(conn, "out of memory allocating SSPI buffer (%d)",
                                                                        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;
        }

        /* finished parsing, trace server-to-client message */
        if (conn->Pfdebug)
                pqTraceOutputMessage(conn, conn->inBuffer + conn->inStart, false);

        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 */
        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)
                {
                        libpq_append_conn_error(conn, "out of memory");
                        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)
                {
                        conn->current_auth_response = AUTH_RESPONSE_GSS;
                        if (pqPacketSend(conn, PqMsg_GSSResponse,
                                                         outbuf.pBuffers[0].pvBuffer, outbuf.pBuffers[0].cbBuffer))
                        {
                                FreeContextBuffer(outbuf.pBuffers[0].pvBuffer);
                                return STATUS_ERROR;
                        }
                }
                FreeContextBuffer(outbuf.pBuffers[0].pvBuffer);
        }

        if (r == SEC_E_OK)
                conn->client_finished_auth = true;

        /* 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)
        {
                libpq_append_conn_error(conn, "duplicate SSPI authentication request");
                return STATUS_ERROR;
        }

        /*
         * Retrieve credentials handle
         */
        conn->sspicred = malloc(sizeof(CredHandle));
        if (conn->sspicred == NULL)
        {
                libpq_append_conn_error(conn, "out of memory");
                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'))
        {
                libpq_append_conn_error(conn, "host name must be specified");
                return STATUS_ERROR;
        }
        conn->sspitarget = malloc(strlen(conn->krbsrvname) + strlen(host) + 2);
        if (!conn->sspitarget)
        {
                libpq_append_conn_error(conn, "out of memory");
                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;
        const char *selected_mechanism;
        PQExpBufferData mechanism_buf;
        char       *password = NULL;
        SASLStatus      status;

        initPQExpBuffer(&mechanism_buf);

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

        if (conn->sasl_state)
        {
                libpq_append_conn_error(conn, "duplicate SASL authentication request");
                goto error;
        }

        /*
         * Parse the list of SASL authentication mechanisms in the
         * AuthenticationSASL message, and select the best mechanism that we
         * support. Mechanisms are 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 USE_SSL
                                /*
                                 * 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;
                                        conn->sasl = &pg_scram_mech;
                                        conn->password_needed = true;
                                }
#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 */
                                {
                                        libpq_append_conn_error(conn, "channel binding is required, but client does not support it");
                                        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.
                                 */
                                libpq_append_conn_error(conn, "server offered SCRAM-SHA-256-PLUS authentication over a non-SSL connection");
                                goto error;
                        }
                }
                else if (strcmp(mechanism_buf.data, SCRAM_SHA_256_NAME) == 0 &&
                                 !selected_mechanism)
                {
                        selected_mechanism = SCRAM_SHA_256_NAME;
                        conn->sasl = &pg_scram_mech;
                        conn->password_needed = true;
                }
        }

        if (!selected_mechanism)
        {
                libpq_append_conn_error(conn, "none of the server's SASL authentication mechanisms are supported");
                goto error;
        }

        if (conn->channel_binding[0] == 'r' &&  /* require */
                strcmp(selected_mechanism, SCRAM_SHA_256_PLUS_NAME) != 0)
        {
                libpq_append_conn_error(conn, "channel binding is required, but server did not offer an authentication method that supports channel binding");
                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 and the selected SASL mechanism needs it.
         */
        if (conn->password_needed && !conn->scram_client_key_binary)
        {
                password = conn->connhost[conn->whichhost].password;
                if (password == NULL)
                        password = conn->pgpass;
                if (password == NULL || password[0] == '\0')
                {
                        appendPQExpBufferStr(&conn->errorMessage,
                                                                 PQnoPasswordSupplied);
                        goto error;
                }
        }

        /* finished parsing, trace server-to-client message */
        if (conn->Pfdebug)
                pqTraceOutputMessage(conn, conn->inBuffer + conn->inStart, false);

        Assert(conn->sasl);

        /*
         * 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 = conn->sasl->init(conn,
                                                                                password,
                                                                                selected_mechanism);
        if (!conn->sasl_state)
                goto oom_error;

        /* Get the mechanism-specific Initial Client Response, if any */
        status = conn->sasl->exchange(conn->sasl_state,
                                                                  NULL, -1,
                                                                  &initialresponse, &initialresponselen);

        if (status == SASL_FAILED)
                goto error;

        /*
         * Build a SASLInitialResponse message, and send it.
         */
        if (pqPutMsgStart(PqMsg_SASLInitialResponse, 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;
        }
        conn->current_auth_response = AUTH_RESPONSE_SASL_INITIAL;
        if (pqPutMsgEnd(conn))
                goto error;

        if (pqFlush(conn))
                goto error;

        termPQExpBuffer(&mechanism_buf);
        free(initialresponse);

        return STATUS_OK;

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

oom_error:
        termPQExpBuffer(&mechanism_buf);
        free(initialresponse);
        libpq_append_conn_error(conn, "out of memory");
        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;
        int                     res;
        char       *challenge;
        SASLStatus      status;

        /* Read the SASL challenge from the AuthenticationSASLContinue message. */
        challenge = malloc(payloadlen + 1);
        if (!challenge)
        {
                libpq_append_conn_error(conn, "out of memory allocating SASL buffer (%d)",
                                                                payloadlen);
                return STATUS_ERROR;
        }

        if (pqGetnchar(challenge, payloadlen, conn))
        {
                free(challenge);
                return STATUS_ERROR;
        }

        /* finished parsing, trace server-to-client message */
        if (conn->Pfdebug)
                pqTraceOutputMessage(conn, conn->inBuffer + conn->inStart, false);

        /* For safety and convenience, ensure the buffer is NULL-terminated. */
        challenge[payloadlen] = '\0';

        status = conn->sasl->exchange(conn->sasl_state,
                                                                  challenge, payloadlen,
                                                                  &output, &outputlen);
        free(challenge);                        /* don't need the input anymore */

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

                libpq_append_conn_error(conn, "AuthenticationSASLFinal received from server, but SASL authentication was not completed");
                return STATUS_ERROR;
        }

        /*
         * If the exchange is not completed yet, we need to make sure that the
         * SASL mechanism has generated a message to send back.
         */
        if (output == NULL && status == SASL_CONTINUE)
        {
                libpq_append_conn_error(conn, "no client response found after SASL exchange success");
                return STATUS_ERROR;
        }

        /*
         * SASL allows zero-length responses, so this check uses "output" and not
         * "outputlen" to allow the case of an empty message.
         */
        if (output)
        {
                /*
                 * Send the SASL response to the server.
                 */
                conn->current_auth_response = AUTH_RESPONSE_SASL;
                res = pqPacketSend(conn, PqMsg_SASLResponse, output, outputlen);
                free(output);

                if (res != STATUS_OK)
                        return STATUS_ERROR;
        }

        if (status == SASL_FAILED)
                return STATUS_ERROR;

        return STATUS_OK;
}

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 */
        }

        /* finished parsing, trace server-to-client message */
        if (conn->Pfdebug)
                pqTraceOutputMessage(conn, conn->inBuffer + conn->inStart, false);

        /* Encrypt the password if needed. */

        switch (areq)
        {
                case AUTH_REQ_MD5:
                        {
                                char       *crypt_pwd2;
                                const char *errstr = NULL;

                                /* Allocate enough space for two MD5 hashes */
                                crypt_pwd = malloc(2 * (MD5_PASSWD_LEN + 1));
                                if (!crypt_pwd)
                                {
                                        libpq_append_conn_error(conn, "out of memory");
                                        return STATUS_ERROR;
                                }

                                crypt_pwd2 = crypt_pwd + MD5_PASSWD_LEN + 1;
                                if (!pg_md5_encrypt(password, conn->pguser,
                                                                        strlen(conn->pguser), crypt_pwd2,
                                                                        &errstr))
                                {
                                        libpq_append_conn_error(conn, "could not encrypt password: %s", errstr);
                                        free(crypt_pwd);
                                        return STATUS_ERROR;
                                }
                                if (!pg_md5_encrypt(crypt_pwd2 + strlen("md5"), md5Salt,
                                                                        4, crypt_pwd, &errstr))
                                {
                                        libpq_append_conn_error(conn, "could not encrypt password: %s", errstr);
                                        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;
        }
        conn->current_auth_response = AUTH_RESPONSE_PASSWORD;
        ret = pqPacketSend(conn, PqMsg_PasswordMessage,
                                           pwd_to_send, strlen(pwd_to_send) + 1);
        free(crypt_pwd);
        return ret;
}

/*
 * Translate a disallowed AuthRequest code into an error message.
 */
static const char *
auth_method_description(AuthRequest areq)
{
        switch (areq)
        {
                case AUTH_REQ_PASSWORD:
                        return libpq_gettext("server requested a cleartext password");
                case AUTH_REQ_MD5:
                        return libpq_gettext("server requested a hashed password");
                case AUTH_REQ_GSS:
                case AUTH_REQ_GSS_CONT:
                        return libpq_gettext("server requested GSSAPI authentication");
                case AUTH_REQ_SSPI:
                        return libpq_gettext("server requested SSPI authentication");
                case AUTH_REQ_SASL:
                case AUTH_REQ_SASL_CONT:
                case AUTH_REQ_SASL_FIN:
                        return libpq_gettext("server requested SASL authentication");
        }

        return libpq_gettext("server requested an unknown authentication type");
}

/*
 * Convenience macro for checking the allowed_auth_methods bitmask.  Caller
 * must ensure that type is not greater than 31 (high bit of the bitmask).
 */
#define auth_method_allowed(conn, type) \
        (((conn)->allowed_auth_methods & (1 << (type))) != 0)

/*
 * 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;
        const char *reason = NULL;

        StaticAssertDecl((sizeof(conn->allowed_auth_methods) * CHAR_BIT) > AUTH_REQ_MAX,
                                         "AUTH_REQ_MAX overflows the allowed_auth_methods bitmask");

        if (conn->sslcertmode[0] == 'r' /* require */
                && areq == AUTH_REQ_OK)
        {
                /*
                 * Trade off a little bit of complexity to try to get these error
                 * messages as precise as possible.
                 */
                if (!conn->ssl_cert_requested)
                {
                        libpq_append_conn_error(conn, "server did not request an SSL certificate");
                        return false;
                }
                else if (!conn->ssl_cert_sent)
                {
                        libpq_append_conn_error(conn, "server accepted connection without a valid SSL certificate");
                        return false;
                }
        }

        /*
         * If the user required a specific auth method, or specified an allowed
         * set, then reject all others here, and make sure the server actually
         * completes an authentication exchange.
         */
        if (conn->require_auth)
        {
                switch (areq)
                {
                        case AUTH_REQ_OK:

                                /*
                                 * Check to make sure we've actually finished our exchange (or
                                 * else that the user has allowed an authentication-less
                                 * connection).
                                 *
                                 * If the user has allowed both SCRAM and unauthenticated
                                 * (trust) connections, then this check will silently accept
                                 * partial SCRAM exchanges, where a misbehaving server does
                                 * not provide its verifier before sending an OK.  This is
                                 * consistent with historical behavior, but it may be a point
                                 * to revisit in the future, since it could allow a server
                                 * that doesn't know the user's password to silently harvest
                                 * material for a brute force attack.
                                 */
                                if (!conn->auth_required || conn->client_finished_auth)
                                        break;

                                /*
                                 * No explicit authentication request was made by the server
                                 * -- or perhaps it was made and not completed, in the case of
                                 * SCRAM -- but there is one special case to check.  If the
                                 * user allowed "gss", then a GSS-encrypted channel also
                                 * satisfies the check.
                                 */
#ifdef ENABLE_GSS
                                if (auth_method_allowed(conn, AUTH_REQ_GSS) && conn->gssenc)
                                {
                                        /*
                                         * If implicit GSS auth has already been performed via GSS
                                         * encryption, we don't need to have performed an
                                         * AUTH_REQ_GSS exchange.  This allows require_auth=gss to
                                         * be combined with gssencmode, since there won't be an
                                         * explicit authentication request in that case.
                                         */
                                }
                                else
#endif
                                {
                                        reason = libpq_gettext("server did not complete authentication");
                                        result = false;
                                }

                                break;

                        case AUTH_REQ_PASSWORD:
                        case AUTH_REQ_MD5:
                        case AUTH_REQ_GSS:
                        case AUTH_REQ_GSS_CONT:
                        case AUTH_REQ_SSPI:
                        case AUTH_REQ_SASL:
                        case AUTH_REQ_SASL_CONT:
                        case AUTH_REQ_SASL_FIN:

                                /*
                                 * We don't handle these with the default case, to avoid
                                 * bit-shifting past the end of the allowed_auth_methods mask
                                 * if the server sends an unexpected AuthRequest.
                                 */
                                result = auth_method_allowed(conn, areq);
                                break;

                        default:
                                result = false;
                                break;
                }
        }

        if (!result)
        {
                if (!reason)
                        reason = auth_method_description(areq);

                libpq_append_conn_error(conn, "authentication method requirement \"%s\" failed: %s",
                                                                conn->require_auth, reason);
                return result;
        }

        /*
         * 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 (!conn->sasl || !conn->sasl->channel_bound(conn->sasl_state))
                                {
                                        libpq_append_conn_error(conn, "channel binding required, but server authenticated client without channel binding");
                                        result = false;
                                }
                                break;
                        default:
                                libpq_append_conn_error(conn, "channel binding required but not supported by server's authentication request");
                                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:
                        libpq_append_conn_error(conn, "Kerberos 4 authentication not supported");
                        return STATUS_ERROR;

                case AUTH_REQ_KRB5:
                        libpq_append_conn_error(conn, "Kerberos 5 authentication not supported");
                        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:
                        libpq_append_conn_error(conn, "GSSAPI authentication not supported");
                        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:
                        libpq_append_conn_error(conn, "SSPI authentication not supported");
                        return STATUS_ERROR;
#endif                                                  /* !define(ENABLE_GSS) */
#endif                                                  /* ENABLE_SSPI */


                case AUTH_REQ_CRYPT:
                        libpq_append_conn_error(conn, "Crypt authentication not supported");
                        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;
                                }

                                /* We expect no further authentication requests. */
                                conn->client_finished_auth = true;
                                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;

                default:
                        libpq_append_conn_error(conn, "authentication method %u not supported", areq);
                        return STATUS_ERROR;
        }

        return STATUS_OK;
}


/*
 * pg_fe_getusername
 *
 * Returns a pointer to malloc'd space containing the name of the
 * specified user_id.  If there is an error, return NULL, and append
 * a suitable error message to *errorMessage if that's not NULL.
 *
 * Caution: on Windows, the user_id argument is ignored, and we always
 * fetch the current user's name.
 */
char *
pg_fe_getusername(uid_t user_id, 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
        struct passwd pwbuf;
        struct passwd *pw = NULL;
        char            buf[1024];
        int                     rc;
#endif

#ifdef WIN32
        if (GetUserName(username, &namesize))
                name = username;
        else if (errorMessage)
                libpq_append_error(errorMessage,
                                                   "user name lookup failure: error code %lu",
                                                   GetLastError());
#else
        rc = getpwuid_r(user_id, &pwbuf, buf, sizeof buf, &pw);
        if (rc != 0)
        {
                errno = rc;
                if (errorMessage)
                        libpq_append_error(errorMessage, "could not look up local user ID %ld: %m", (long) user_id);
        }
        else if (!pw)
        {
                if (errorMessage)
                        libpq_append_error(errorMessage, "local user with ID %ld does not exist", (long) user_id);
        }
        else
                name = pw->pw_name;
#endif

        if (name)
        {
                result = strdup(name);
                if (result == NULL && errorMessage)
                        libpq_append_error(errorMessage, "out of memory");
        }

        return result;
}

/*
 * 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)
{
#ifdef WIN32
        return pg_fe_getusername(0, errorMessage);
#else
        return pg_fe_getusername(geteuid(), errorMessage);
#endif
}


/*
 * 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;
        const char *errstr = NULL;

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

        if (!pg_md5_encrypt(passwd, user, strlen(user), crypt_pwd, &errstr))
        {
                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;

        pqClearConnErrorState(conn);

        /* 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);
                        libpq_append_conn_error(conn, "unexpected shape of result set returned for SHOW");
                        return NULL;
                }
                val = PQgetvalue(res, 0, 0);

                if (strlen(val) > MAX_ALGORITHM_NAME_LEN)
                {
                        PQclear(res);
                        libpq_append_conn_error(conn, "\"password_encryption\" value too long");
                        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)
        {
                const char *errstr = NULL;

                crypt_pwd = pg_fe_scram_build_secret(passwd,
                                                                                         conn->scram_sha_256_iterations,
                                                                                         &errstr);
                if (!crypt_pwd)
                        libpq_append_conn_error(conn, "could not encrypt password: %s", errstr);
        }
        else if (strcmp(algorithm, "md5") == 0)
        {
                crypt_pwd = malloc(MD5_PASSWD_LEN + 1);
                if (crypt_pwd)
                {
                        const char *errstr = NULL;

                        if (!pg_md5_encrypt(passwd, user, strlen(user), crypt_pwd, &errstr))
                        {
                                libpq_append_conn_error(conn, "could not encrypt password: %s", errstr);
                                free(crypt_pwd);
                                crypt_pwd = NULL;
                        }
                }
                else
                        libpq_append_conn_error(conn, "out of memory");
        }
        else
        {
                libpq_append_conn_error(conn, "unrecognized password encryption algorithm \"%s\"",
                                                                algorithm);
                return NULL;
        }

        return crypt_pwd;
}

/*
 * PQchangePassword -- exported routine to change a password
 *
 * This is intended to be used by client applications that wish to
 * change the password for a user. The password is not sent in
 * cleartext because it is encrypted on the client side. This is
 * good because it ensures the cleartext password is never known by
 * the server, and therefore won't end up in logs, pg_stat displays,
 * etc. The password encryption is performed by PQencryptPasswordConn(),
 * which is passed a NULL for the algorithm argument. Hence encryption
 * is done according to the server's password_encryption
 * setting. We export the function so that clients won't be dependent
 * on the implementation specific details with respect to how the
 * server changes passwords.
 *
 * Arguments are a connection object, the SQL name of the target user,
 * and the cleartext password.
 *
 * Return value is the PGresult of the executed ALTER USER statement
 * or NULL if we never get there. The caller is responsible to PQclear()
 * the returned PGresult.
 *
 * PQresultStatus() should be called to check the return value for errors,
 * and PQerrorMessage() used to get more information about such errors.
 */
PGresult *
PQchangePassword(PGconn *conn, const char *user, const char *passwd)
{
        char       *encrypted_password = PQencryptPasswordConn(conn, passwd,
                                                                                                                   user, NULL);

        if (!encrypted_password)
        {
                /* PQencryptPasswordConn() already registered the error */
                return NULL;
        }
        else
        {
                char       *fmtpw = PQescapeLiteral(conn, encrypted_password,
                                                                                        strlen(encrypted_password));

                /* no longer needed, so clean up now */
                PQfreemem(encrypted_password);

                if (!fmtpw)
                {
                        /* PQescapeLiteral() already registered the error */
                        return NULL;
                }
                else
                {
                        char       *fmtuser = PQescapeIdentifier(conn, user, strlen(user));

                        if (!fmtuser)
                        {
                                /* PQescapeIdentifier() already registered the error */
                                PQfreemem(fmtpw);
                                return NULL;
                        }
                        else
                        {
                                PQExpBufferData buf;
                                PGresult   *res;

                                initPQExpBuffer(&buf);
                                printfPQExpBuffer(&buf, "ALTER USER %s PASSWORD %s",
                                                                  fmtuser, fmtpw);

                                res = PQexec(conn, buf.data);

                                /* clean up */
                                termPQExpBuffer(&buf);
                                PQfreemem(fmtuser);
                                PQfreemem(fmtpw);

                                return res;
                        }
                }
        }
}