protected function cartIdentifier()
    {
        // If auth user is set manually, use it
        if (app()->offsetExists('cart_auth_user_id')) {
            return ['auth_user' => resolve('cart_auth_user_id')];
        }

        // If customer is logged in, use his identifier
        if (Auth::guard(config('cart_manager.auth_guard'))->check()) {
            return ['auth_user' => Auth::guard(config('cart_manager.auth_guard'))->id()];
        }

        return $this->getCookieElement();
    }