Warn on password auth with MD5-encrypted passwords

Commit bc60ee860 added a connection warning after successful MD5
authentication, but only for the md5 authentication method. A role with
an MD5-encrypted password can also authenticate via the password method,
which left that path without the same deprecation warning.

Emit the MD5 deprecation connection warning after successful
password authentication as well, when the stored password is
MD5-encrypted.

Backpatch to v19, where the MD5 connection warning was introduced.

Author: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Japin Li <japinli@hotmail.com>
Discussion: https://postgr.es/m/CAHGQGwGkWfn5rtHzvdRbVk+PCefQU3gun3hc7QnaMXHFa5Bu3w@mail.gmail.com
Backpatch-through: 19

doc/src/sgml/config.sgml

@@ -1206,7 +1206,8 @@ include_dir 'conf.d'
       <listitem>
        <para>
         Controls whether a <literal>WARNING</literal> about MD5 password
-        deprecation is produced upon successful MD5 password authentication or
+        deprecation is produced upon successful authentication using an
+        MD5-encrypted password or
         when a <command>CREATE ROLE</command> or
         <command>ALTER ROLE</command> statement sets an MD5-encrypted password.
         The default value is <literal>on</literal>.

src/backend/libpq/auth.c

@@ -48,6 +48,8 @@
 static void auth_failed(Port *port, int elevel, int status,
 						const char *logdetail);
 static char *recv_password_packet(Port *port);
+static bool md5_password_warning_enabled(void);
+static void queue_md5_password_warning(void);
 
 
 /*----------------------------------------------------------------
@@ -795,6 +797,7 @@ CheckPasswordAuth(Port *port, const char **logdetail)
 	char	   *passwd;
 	int			result;
 	char	   *shadow_pass;
+	bool		md5_password = false;
 
 	sendAuthRequest(port, AUTH_REQ_PASSWORD, NULL, 0);
 
@@ -807,6 +810,7 @@ CheckPasswordAuth(Port *port, const char **logdetail)
 	{
 		result = plain_crypt_verify(port->user_name, shadow_pass, passwd,
 									logdetail);
+		md5_password = (get_password_type(shadow_pass) == PASSWORD_TYPE_MD5);
 	}
 	else
 		result = STATUS_ERROR;
@@ -816,7 +820,11 @@ CheckPasswordAuth(Port *port, const char **logdetail)
 	pfree(passwd);
 
 	if (result == STATUS_OK)
+	{
+		if (md5_password)
+			queue_md5_password_warning();
 		set_authn_id(port, port->user_name);
+	}
 
 	return result;
 }
@@ -913,9 +921,34 @@ CheckMD5Auth(Port *port, char *shadow_pass, const char **logdetail)
 
 	pfree(passwd);
 
+	if (result == STATUS_OK)
+		queue_md5_password_warning();
+
 	return result;
 }
 
+static bool
+md5_password_warning_enabled(void)
+{
+	return md5_password_warnings;
+}
+
+static void
+queue_md5_password_warning(void)
+{
+	MemoryContext oldcontext;
+	char	   *warning;
+	char	   *detail;
+
+	oldcontext = MemoryContextSwitchTo(TopMemoryContext);
+
+	warning = pstrdup(_("authenticated with an MD5-encrypted password"));
+	detail = pstrdup(_("MD5 password support is deprecated and will be removed in a future release of PostgreSQL."));
+	StoreConnectionWarning(warning, detail, md5_password_warning_enabled);
+
+	MemoryContextSwitchTo(oldcontext);
+}
+
 
 /*----------------------------------------------------------------
  * GSSAPI authentication system

src/backend/libpq/crypt.c

@@ -32,8 +32,6 @@ int			password_expiration_warning_threshold = 604800;
 /* Enables deprecation warnings for MD5 passwords. */
 bool		md5_password_warnings = true;
 
-static bool md5_password_warning_enabled(void);
-
 /*
  * Fetch stored password for a user, for authentication.
  *
@@ -297,21 +295,7 @@ md5_crypt_verify(const char *role, const char *shadow_pass,
 
 	if (strlen(client_pass) == strlen(crypt_pwd) &&
 		timingsafe_bcmp(client_pass, crypt_pwd, strlen(crypt_pwd)) == 0)
-	{
-		MemoryContext oldcontext;
-		char	   *warning;
-		char	   *detail;
-
 		retval = STATUS_OK;
-
-		oldcontext = MemoryContextSwitchTo(TopMemoryContext);
-
-		warning = pstrdup(_("authenticated with an MD5-encrypted password"));
-		detail = pstrdup(_("MD5 password support is deprecated and will be removed in a future release of PostgreSQL."));
-		StoreConnectionWarning(warning, detail, md5_password_warning_enabled);
-
-		MemoryContextSwitchTo(oldcontext);
-	}
 	else
 	{
 		*logdetail = psprintf(_("Password does not match for user \"%s\"."),
@@ -322,12 +306,6 @@ md5_crypt_verify(const char *role, const char *shadow_pass,
 	return retval;
 }
 
-static bool
-md5_password_warning_enabled(void)
-{
-	return md5_password_warnings;
-}
-
 /*
  * Check given password for given user, and return STATUS_OK or STATUS_ERROR.
  *

src/test/authentication/t/001_password.pl

@@ -385,9 +385,19 @@ SKIP:
 {
 	skip "MD5 not supported" unless $md5_works;
 	test_conn($node, 'user=md5_role', 'password', 0,
+		expected_stderr => qr/authenticated with an MD5-encrypted password/,
 		log_like =>
 		  [qr/connection authenticated: identity="md5_role" method=password/]
 	);
+
+	$node->connect_ok(
+		'user=md5_role_no_warnings',
+		'password with warnings disabled',
+		sql => 'SHOW md5_password_warnings',
+		expected_stdout => qr/^off$/,
+		log_like => [
+			qr/connection authenticated: identity="md5_role_no_warnings" method=password/
+		]);
 }
 
 # require_auth succeeds here with a plaintext password.