Merge pull request #18333 from nextcloud/backport/18312/stable16

[stable16] Do not disable authentication apps

Author: rullzer

lib/private/legacy/app.php

@@ -158,8 +158,9 @@ public static function loadApp(string $app) {
 					throw $ex;
 				}
 				\OC::$server->getLogger()->logException($ex);
-				if (!\OC::$server->getAppManager()->isShipped($app)) {
-					// Only disable apps which are not shipped
+
+				if (!\OC::$server->getAppManager()->isShipped($app) && !self::isType($app, ['authentication'])) {
+					// Only disable apps which are not shipped and that are not authentication apps
 					\OC::$server->getAppManager()->disableApp($app, true);
 				}
 			}