pgsql: De-Revert "Add support for Kerberos credential delegation"

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

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/6633cfb21691840c33816a6dacaca0b504efb895

Modified Files
--------------
contrib/dblink/dblink.c                        | 127 ++++++----
contrib/dblink/expected/dblink.out             |   4 +-
contrib/postgres_fdw/connection.c              |  72 ++++--
contrib/postgres_fdw/expected/postgres_fdw.out |  19 +-
contrib/postgres_fdw/option.c                  |   6 +
contrib/postgres_fdw/sql/postgres_fdw.sql      |   3 +-
doc/src/sgml/config.sgml                       |  17 ++
doc/src/sgml/dblink.sgml                       |   5 +-
doc/src/sgml/libpq.sgml                        |  41 +++
doc/src/sgml/monitoring.sgml                   |   9 +
doc/src/sgml/postgres-fdw.sgml                 |   7 +-
src/backend/catalog/system_views.sql           |   3 +-
src/backend/foreign/foreign.c                  |   1 +
src/backend/libpq/auth.c                       |  13 +-
src/backend/libpq/be-gssapi-common.c           |  53 ++++
src/backend/libpq/be-secure-gssapi.c           |  26 +-
src/backend/utils/activity/backend_status.c    |   1 +
src/backend/utils/adt/pgstatfuncs.c            |  21 +-
src/backend/utils/init/postinit.c              |   8 +-
src/backend/utils/misc/guc_tables.c            |  10 +
src/backend/utils/misc/postgresql.conf.sample  |   1 +
src/include/catalog/pg_proc.dat                |   6 +-
src/include/libpq/auth.h                       |   1 +
src/include/libpq/be-gssapi-common.h           |   3 +
src/include/libpq/libpq-be.h                   |   2 +
src/include/utils/backend_status.h             |   1 +
src/interfaces/libpq/exports.txt               |   1 +
src/interfaces/libpq/fe-auth.c                 |  15 +-
src/interfaces/libpq/fe-connect.c              |  17 ++
src/interfaces/libpq/fe-secure-gssapi.c        |  23 +-
src/interfaces/libpq/libpq-fe.h                |   1 +
src/interfaces/libpq/libpq-int.h               |   2 +
src/test/kerberos/Makefile                     |   3 +
src/test/kerberos/t/001_auth.pl                | 331 ++++++++++++++++++++++---
src/test/perl/PostgreSQL/Test/Utils.pm         |  27 ++
src/test/regress/expected/rules.out            |  11 +-
36 files changed, 755 insertions(+), 136 deletions(-)