code: func (wxa *MiniProgram) Code2Session(jsCode string) (result ResCode2Session, err error) {
  	urlStr := fmt.Sprintf(code2SessionURL, wxa.AppID, wxa.AppSecret, jsCode)
  	var response []byte
  	response, err = util.HTTPGet(urlStr)
  	if err != nil {
  		return
  	}
  	err = json.Unmarshal(response, &result)
  	if err != nil {
  		return
  	}
  	if result.ErrCode != 0 {
  		err = fmt.Errorf("Code2Session error : errcode=%v , errmsg=%v", result.ErrCode, result.ErrMsg)
  		return
  	}
  	return
  }
docs: // Code2Session 登录凭证校验