Add support for Kerberos credential delegation

Support GSSAPI/Kerberos credentials being delegated to the server by a
client.  With this, a user authenticating to PostgreSQL using Kerberos
(GSSAPI) credentials can choose to delegate their credentials to the
PostgreSQL server (which can choose to accept them, or not), allowing
the server to then use those delegated credentials to connect to
another service, such as with postgres_fdw or dblink or theoretically
any other service which is able to be authenticated using Kerberos.

Both postgres_fdw and dblink are changed to allow non-superuser
password-less connections but only when GSSAPI credentials have been
delegated to the server by the client and GSSAPI is used to
authenticate to the remote system.

Authors: Stephen Frost, Peifeng Qiu
Reviewed-By: David Christensen
Discussion: https://postgr.es/m/CO1PR05MB8023CC2CB575E0FAAD7DF4F8A8E29@CO1PR05MB8023.namprd05.prod.outlook.com

1 files changed, 17 insertions, 0 deletions

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 40fef0e2c81..fcd3d0d9a35 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -343,6 +343,10 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 		"GSS-library", "", 7,	/* sizeof("gssapi") == 7 */
 	offsetof(struct pg_conn, gsslib)},
 
+	{"gssdeleg", "PGGSSDELEG", NULL, NULL,
+		"GSS-delegation", "", 8,	/* sizeof("disable") == 8 */
+	offsetof(struct pg_conn, gssdeleg)},
+
 	{"replication", NULL, NULL, NULL,
 		"Replication", "D", 5,
 	offsetof(struct pg_conn, replication)},
@@ -617,6 +621,7 @@ pqDropServerData(PGconn *conn)
 	conn->auth_req_received = false;
 	conn->client_finished_auth = false;
 	conn->password_needed = false;
+	conn->gssapi_used = false;
 	conn->write_failed = false;
 	free(conn->write_err_msg);
 	conn->write_err_msg = NULL;
@@ -4448,6 +4453,7 @@ freePGconn(PGconn *conn)
 	free(conn->gssencmode);
 	free(conn->krbsrvname);
 	free(conn->gsslib);
+	free(conn->gssdeleg);
 	free(conn->connip);
 	/* Note that conn->Pfdebug is not ours to close or free */
 	free(conn->write_err_msg);
@@ -7313,6 +7319,17 @@ PQconnectionUsedPassword(const PGconn *conn)
 }
 
 int
+PQconnectionUsedGSSAPI(const PGconn *conn)
+{
+	if (!conn)
+		return false;
+	if (conn->gssapi_used)
+		return true;
+	else
+		return false;
+}
+
+int
 PQclientEncoding(const PGconn *conn)
 {
 	if (!conn || conn->status != CONNECTION_OK)