/**
  *
  * @return \conquer\oauth2\models\RefreshToken
  */
 public function getRefreshToken()
 {
     if (is_null($this->_refreshToken)) {
         if (empty($this->refresh_token)) {
             $this->errorServer('The request is missing "refresh_token" parameter');
         }
         if (!($this->_refreshToken = \conquer\oauth2\models\RefreshToken::findOne(['refresh_token' => $this->refresh_token]))) {
             $this->errorServer('The Refresh Token is invalid');
         }
     }
     return $this->_refreshToken;
 }