fix(admin role): fix old and wrong way to determine whether user is admin

- fixes Settings knowing who is an admin of non-local group backend groups
- obsoletes and removes a little old, deprecated code
- double checks proper parameter type on Group\Manager::isAdmin
- also fixes legacy OC_User code to check whether user is an admin

Signed-off-by: Arthur Schiwon <blizzz@arthur-schiwon.de>

1 files changed, 2 insertions, 1 deletions

diff --git a/lib/private/Group/Manager.php b/lib/private/Group/Manager.php
index eb9daebb222..dafbe4295a4 100644
--- a/lib/private/Group/Manager.php
+++ b/lib/private/Group/Manager.php
@@ -52,6 +52,7 @@ use OCP\IGroup;
 use OCP\IGroupManager;
 use OCP\IUser;
 use Psr\Log\LoggerInterface;
+use function is_string;
 
 /**
  * Class Manager
@@ -356,7 +357,7 @@ class Manager extends PublicEmitter implements IGroupManager {
 	 */
 	public function isAdmin($userId) {
 		foreach ($this->backends as $backend) {
-			if ($backend->implementsActions(Backend::IS_ADMIN) && $backend->isAdmin($userId)) {
+			if (is_string($userId) && $backend->implementsActions(Backend::IS_ADMIN) && $backend->isAdmin($userId)) {
 				return true;
 			}
 		}