pgsql: Refactor client-side SSL certificate checking code

Refactor client-side SSL certificate checking code

Separate the parts specific to the SSL library from the general logic.

The previous code structure was

open_client_SSL()
calls verify_peer_name_matches_certificate()
calls verify_peer_name_matches_certificate_name()
calls wildcard_certificate_match()

and was completely in fe-secure-openssl.c.  The new structure is

open_client_SSL() [openssl]
calls pq_verify_peer_name_matches_certificate() [generic]
calls pgtls_verify_peer_name_matches_certificate_guts() [openssl]
calls openssl_verify_peer_name_matches_certificate_name() [openssl]
calls pq_verify_peer_name_matches_certificate_name() [generic]
calls wildcard_certificate_match() [generic]

Move the generic functions into a new file fe-secure-common.c, so the
calls generally go fe-connect.c -> fe-secure.c -> fe-secure-${impl}.c ->
fe-secure-common.c, although there is a bit of back-and-forth between
the last two.

Reviewed-by: Michael Paquier <michael.paquier@gmail.com>

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/f75a95915528646cbfaf238fb48b3ffa17969383

Modified Files
--------------
src/interfaces/libpq/Makefile            |   2 +-
src/interfaces/libpq/fe-secure-common.c  | 204 ++++++++++++++++++++++++++++++
src/interfaces/libpq/fe-secure-common.h  |  26 ++++
src/interfaces/libpq/fe-secure-openssl.c | 210 ++++---------------------------
src/interfaces/libpq/libpq-int.h         |  13 ++
src/interfaces/libpq/nls.mk              |   2 +-
src/tools/msvc/Mkvcbuild.pm              |   1 +
7 files changed, 271 insertions(+), 187 deletions(-)