code: func (ctx *Context) GetQyAccessTokenFromServer() (resQyAccessToken ResQyAccessToken, err error) {
  	log.Printf("GetQyAccessTokenFromServer")
  	url := fmt.Sprintf(qyAccessTokenURL, ctx.AppID, ctx.AppSecret)
  	var body []byte
  	body, err = util.HTTPGet(url)
  	if err != nil {
  		return
  	}
  	err = json.Unmarshal(body, &resQyAccessToken)
  	if err != nil {
  		return
  	}
  	if resQyAccessToken.ErrCode != 0 {
  		err = fmt.Errorf("get qy_access_token error : errcode=%v , errormsg=%v", resQyAccessToken.ErrCode, resQyAccessToken.ErrMsg)
  		return
  	}
  
  	qyAccessTokenCacheKey := fmt.Sprintf("qy_access_token_%s", ctx.AppID)
  	expires := resQyAccessToken.ExpiresIn - 1500
  	err = ctx.Cache.Set(qyAccessTokenCacheKey, resQyAccessToken.AccessToken, time.Duration(expires)*time.Second)
  	return
  }
docs: //GetQyAccessTokenFromServer 强制从微信服务器获取token