public function authenticate($attribute,$params)
    {
        if(!$this->hasErrors())
        {
            $this->_identity = new UserIdentity($this->email, $this->password);
            $this->_identity->authenticate();

      switch($this->_identity->errorCode) {
        case UserIdentity::ERROR_NONE:

            Yii::app()->user->login($this->_identity);
            //Note: I don't see the point of logging in here - this method is
            //just responsible for authentication of the password

            break;
        case UserIdentity::ERROR_USERNAME_INVALID:
            $this->addError('email','Email address is incorrect.');
            break;
        default: // UserIdentity::ERROR_PASSWORD_INVALID
            $this->addError('password','Password is incorrect.');
            break;
      }

        }
    }

    /**
     * Logs in the user using the given username and password in the model.
     * @return boolean whether login is successful
     */
    public function login()
    {
        if($this->_identity === null)
        {
            $this->_identity = new UserIdentity($this->email, $this->password);
            $this->_identity->authenticate();
        }

        if($this->_identity->errorCode === UserIdentity::ERROR_NONE)
        {
            $duration = $this->rememberMe ? 3600*24*30 : 0; // 30 days
            Yii::app()->user->login($this->_identity, $duration);

            return true;
        }
        else
            return false;
    }