public function actionRegister($params = [])
 {
     if (!Student::isAuthorized()) {
         if (isset($_POST) && !empty($_POST)) {
             $student = new Student();
             // TODO: validate user input
             // TODO: use md5() for password
             $student->loadModelFromPost();
             $student->insert();
             Router::redirect('/');
         }
         $this->render('register.php');
     } else {
         Router::error('403');
     }
 }