De-Revert "Add support for Kerberos credential delegation"

This reverts commit 3d03b24c3 (Revert Add support for Kerberos
credential delegation) which was committed on the grounds of concern
about portability, but on further review and discussion, it's clear that
we are better off explicitly requiring MIT Kerberos as that appears to
be the only GSSAPI library currently that's under proper maintenance
and ongoing development.  The API used for storing credentials was added
to MIT Kerberos over a decade ago while for the other libraries which
appear to be mainly based on Heimdal, which exists explicitly to be a
re-implementation of MIT Kerberos, the API never made it to a released
version (even though it was added to the Heimdal git repo over 5 years
ago..).

This post-feature-freeze change was approved by the RMT.

Discussion: https://postgr.es/m/ZDDO6jaESKaBgej0%40tamriel.snowman.net

5 files changed, 74 insertions, 5 deletions

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index f81c2045ec..091a79d4f3 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1190,6 +1190,23 @@ include_dir 'conf.d'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-gss-accept-deleg" xreflabel="gss_accept_deleg">
+      <term><varname>gss_accept_deleg</varname> (<type>boolean</type>)
+      <indexterm>
+       <primary><varname>gss_accept_deleg</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Sets whether GSSAPI delegation should be accepted from the client.
+        The default is <literal>off</literal> meaning credentials from the client will
+        NOT be accepted.  Changing this to <literal>on</literal> will make the server
+        accept credentials delegated to it from the client. This parameter can only be
+        set in the <filename>postgresql.conf</filename> file or on the server command line.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-db-user-namespace" xreflabel="db_user_namespace">
       <term><varname>db_user_namespace</varname> (<type>boolean</type>)
       <indexterm>
diff --git a/doc/src/sgml/dblink.sgml b/doc/src/sgml/dblink.sgml
index 17f9d99b1c..7d25f24f49 100644
--- a/doc/src/sgml/dblink.sgml
+++ b/doc/src/sgml/dblink.sgml
@@ -117,8 +117,9 @@ dblink_connect(text connname, text connstr) returns text
 
    <para>
     Only superusers may use <function>dblink_connect</function> to create
-    non-password-authenticated connections.  If non-superusers need this
-    capability, use <function>dblink_connect_u</function> instead.
+    non-password-authenticated and non-GSSAPI-authenticated connections.
+    If non-superusers need this capability, use
+    <function>dblink_connect_u</function> instead.
    </para>
 
    <para>
diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index faa8aa3187..b8702284d0 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -2054,6 +2054,18 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       </listitem>
      </varlistentry>
 
+     <varlistentry id="libpq-connect-gssdeleg" xreflabel="gssdeleg">
+      <term><literal>gssdeleg</literal></term>
+      <listitem>
+       <para>
+        Forward (delegate) GSS credentials to the server.  The default is
+        <literal>disable</literal> which means credentials will not be forwarded
+        to the server.  Set this to <literal>enable</literal> to have
+        credentials forwarded when possible.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="libpq-connect-service" xreflabel="service">
       <term><literal>service</literal></term>
       <listitem>
@@ -2715,6 +2727,25 @@ int PQconnectionUsedPassword(const PGconn *conn);
       </para>
      </listitem>
     </varlistentry>
+
+    <varlistentry id="libpq-PQconnectionUsedGSSAPI">
+     <term><function>PQconnectionUsedGSSAPI</function><indexterm><primary>PQconnectionUsedGSSAPI</primary></indexterm></term>
+     <listitem>
+      <para>
+       Returns true (1) if the connection authentication method
+       used GSSAPI. Returns false (0) if not.
+
+<synopsis>
+int PQconnectionUsedGSSAPI(const PGconn *conn);
+</synopsis>
+      </para>
+
+      <para>
+       This function can be applied to detect whether the connection was
+       authenticated with GSSAPI.
+      </para>
+     </listitem>
+    </varlistentry>
    </variablelist>
   </para>
 
@@ -8240,6 +8271,16 @@ myEventProc(PGEventId evtId, void *evtInfo, void *passThrough)
     <listitem>
      <para>
       <indexterm>
+       <primary><envar>PGGSSDELEG</envar></primary>
+      </indexterm>
+      <envar>PGGSSDELEG</envar> behaves the same as the <xref
+      linkend="libpq-connect-gssdeleg"/> connection parameter.
+     </para>
+    </listitem>
+
+    <listitem>
+     <para>
+      <indexterm>
        <primary><envar>PGCONNECT_TIMEOUT</envar></primary>
       </indexterm>
       <envar>PGCONNECT_TIMEOUT</envar>  behaves the same as the <xref
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index c95b879f31..0281201745 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3581,6 +3581,15 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
        True if GSSAPI encryption is in use on this connection
       </para></entry>
      </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>credentials_delegated</structfield> <type>boolean</type>
+      </para>
+      <para>
+       True if GSSAPI credentials were delegated on this connection.
+      </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>
diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml
index a122794df3..b9a5b0eac8 100644
--- a/doc/src/sgml/postgres-fdw.sgml
+++ b/doc/src/sgml/postgres-fdw.sgml
@@ -169,9 +169,10 @@
     <literal>sslcert</literal> or <literal>sslkey</literal> settings.
    </para>
    <para>
-    Only superusers may connect to foreign servers without password
-    authentication, so always specify the <literal>password</literal> option
-    for user mappings belonging to non-superusers.
+    Non-superusers may connect to foreign servers using password
+    authentication or with GSSAPI delegated credentials, so specify the
+    <literal>password</literal> option for user mappings belonging to
+    non-superusers where password authentication is required.
    </para>
    <para>
     A superuser may override this check on a per-user-mapping basis by setting