public function loginAction()
 {
     $flash = '';
     if (Identity::isAuthenticated()) {
         return $this->redirect('/followings');
     } else {
         if (isset($_POST['username']) && isset($_POST['password'])) {
             try {
                 Identity::authenticate($_POST['username'], $_POST['password']);
             } catch (\Exception $e) {
                 $flash = $e->getMessage();
             }
             if (Identity::isAuthenticated()) {
                 return $this->redirect('/followings');
             } else {
                 $flash .= "Authentication failed. Please try again.";
             }
         }
     }
     return new ViewModel('user/login.phtml', array('flash' => $flash));
 }