yii\web\Controller::beforeAction PHP Method

    public function beforeAction($action)
    {
        if (parent::beforeAction($action)) {
            if ($this->enableCsrfValidation && Yii::$app->getErrorHandler()->exception === null && !Yii::$app->getRequest()->validateCsrfToken()) {
                throw new BadRequestHttpException(Yii::t('yii', 'Unable to verify your data submission.'));
            }
            return true;
        }
        return false;
    }

 public function beforeAction($action)
 {
     if ($action->id == 'index' && Yii::$app->request->referrer !== null) {
         Yii::$app->session->set('returnUrl', Yii::$app->request->referrer);
     }
     return parent::beforeAction($action);
 }