/**
  * Display a listing of the resource.
  *
  * @param $instance_id
  * @return \Illuminate\Http\Response
  */
 public function index($instance_id)
 {
     // If user has not permission to list users, log it and deny access (HTTP 403)
     if (Gate::denies('list-instance-users', [User::class, $instance_id])) {
         Log::info('Access denied for instance user listing.', ['auth_user' => auth()->user(), 'request_ip' => request()->ip(), 'instance_id' => $instance_id]);
         abort(403);
     }
     return response()->json(User::fromInstance($instance_id)->get());
 }