Add authentication TAP test for peer authentication

This commit introduces an authentication test for the peer method, as of
a set of scenarios with and without a user name map.  The script is
automatically skipped if peer is not supported in the environment where
this test is run, checking this behavior by attempting a connection
first on a cluster up and running.

Author: Bertrand Drouvot
Discussion: https://postgr.es/m/aa60994b-1c66-ca7a-dab9-9a200dbac3d2@amazon.com

src/test/authentication/meson.build

@@ -6,6 +6,7 @@ tests += {
     'tests': [
       't/001_password.pl',
       't/002_saslprep.pl',
+      't/003_peer.pl',
     ],
   },
 }

src/test/authentication/t/003_peer.pl

@@ -0,0 +1,102 @@
+
+# Copyright (c) 2021-2022, PostgreSQL Global Development Group
+
+# Tests for peer authentication and user name map.
+# The test is skipped if the platform does not support peer authentication.
+
+use strict;
+use warnings;
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Delete pg_hba.conf from the given node, add a new entry to it
+# and then execute a reload to refresh it.
+sub reset_pg_hba
+{
+	my $node       = shift;
+	my $hba_method = shift;
+
+	unlink($node->data_dir . '/pg_hba.conf');
+	$node->append_conf('pg_hba.conf', "local all all $hba_method");
+	$node->reload;
+	return;
+}
+
+# Test access for a single role, useful to wrap all tests into one.
+sub test_role
+{
+	local $Test::Builder::Level = $Test::Builder::Level + 1;
+
+	my ($node, $role, $method, $expected_res, %params) = @_;
+	my $status_string = 'failed';
+	$status_string = 'success' if ($expected_res eq 0);
+
+	my $connstr = "user=$role";
+	my $testname =
+	  "authentication $status_string for method $method, role $role";
+
+	if ($expected_res eq 0)
+	{
+		$node->connect_ok($connstr, $testname, %params);
+	}
+	else
+	{
+		# No checks of the error message, only the status code.
+		$node->connect_fails($connstr, $testname, %params);
+	}
+}
+
+# Find $pattern in log file of $node.
+sub find_in_log
+{
+	my ($node, $offset, $pattern) = @_;
+
+	my $log = PostgreSQL::Test::Utils::slurp_file($node->logfile, $offset);
+	return 0 if (length($log) <= 0);
+
+	return $log =~ m/$pattern/;
+}
+
+my $node = PostgreSQL::Test::Cluster->new('node');
+$node->init;
+$node->append_conf('postgresql.conf', "log_connections = on\n");
+$node->start;
+
+# Set pg_hba.conf with the peer authentication.
+reset_pg_hba($node, 'peer');
+
+# Check if peer authentication is supported on this platform.
+my $log_offset = -s $node->logfile;
+$node->psql('postgres');
+if (find_in_log(
+		$node, $log_offset,
+		qr/peer authentication is not supported on this platform/))
+{
+	plan skip_all => 'peer authentication is not supported on this platform';
+}
+
+# Add a database role, to use for the user name map.
+$node->safe_psql('postgres', qq{CREATE ROLE testmapuser LOGIN});
+
+# Extract as well the system user for the user name map.
+my $system_user =
+  $node->safe_psql('postgres',
+	q(select (string_to_array(SYSTEM_USER, ':'))[2]));
+
+# Tests without the user name map.
+# Failure as connection is attempted with a database role not mapping
+# to an authorized system user.
+test_role($node, qq{testmapuser}, 'peer', 2,
+	log_like => [qr/Peer authentication failed for user "testmapuser"/]);
+
+# Tests with a user name map.
+$node->append_conf('pg_ident.conf', qq{mypeermap $system_user testmapuser});
+reset_pg_hba($node, 'peer map=mypeermap');
+
+# Success as the database role matches with the system user in the map.
+test_role($node, qq{testmapuser}, 'peer', 0,
+	log_like =>
+	  [qr/connection authenticated: identity="$system_user" method=peer/]);
+
+done_testing();