public function weixinCallback()
 {
     if (Input::get('state') !== 'STATE') {
         // todo
         return;
     }
     $this->type = 'weixin';
     $openId = $this->getOpenId();
     $result = $this->hasOpenId($openId);
     if ($result) {
         return 'See open id ' . $result;
     }
     // 拉取第三方用户信息
     $user = $this->fetchUser($openId);
     $avatarUrl = $user->headimgurl;
     $tmpToken = MultiplexController::temporaryToken();
     $this->storeOpenId($openId, $tmpToken);
     return 'QueryString ?avatar_url=' . $avatarUrl . '&token=' . $tmpToken;
 }