fix: use userId in ban filter

lib/Auth/Process/IsBanned.php

@@ -75,11 +75,12 @@ class IsBanned extends ProcessingFilter
             );
         }
 
-        if ($this->banExists($user)) {
-            Logger::info('perun:IsBanned: user ' . $user . ' is banned, redirecting to configured URL');
+        $userId =  $user->getId();
+        if ($this->banExists($userId)) {
+            Logger::info('perun:IsBanned: user ' . $userId . ' is banned, redirecting to configured URL');
             HTTP::redirectTrustedURL($this->redirectUrl);
         } else {
-            Logger::debug('perun:IsBanned: user ' . $user . ' is not banned');
+            Logger::debug('perun:IsBanned: user ' . $userId . ' is not banned');
         }
     }