CI accessing property on interface
To fix the problem for the id of the authenticated user, you should use:
$this->auth->user()->getAuthIdentifier()Interface consists of methods. You are accessing attribute directly. eg $foo->id instead of $foo->getId(). And you have to add new method to interface of course.
The workaround is to say to scrutinizer, that $object is instance of desired class.
if ($object instanceof MyClass) { //}