OneSignal\Config::setApplicationId PHP Method

    public function setApplicationId($applicationId)
    {
        $this->applicationId = $applicationId;
    }

 public function register()
 {
     $this->app->singleton('onesignal', function ($app) {
         $settings = $app['config']->get('services.onesignal');
         $config = new Config();
         $config->setApplicationId($settings['app_id']);
         $config->setApplicationAuthKey($settings['app_key']);
         $config->setUserAuthKey($settings['user_key']);
         return new OneSignal($config);
     });
 }