code: func (user *User) ListUserOpenIDs(nextOpenid ...string) (*OpenidList, error) {
  	accessToken, err := user.GetAccessToken()
  	if err != nil {
  		return nil, err
  	}
  
  	uri, _ := url.Parse(userListURL)
  	q := uri.Query()
  	q.Set("access_token", accessToken)
  	if len(nextOpenid) > 0 && nextOpenid[0] != "" {
  		q.Set("next_openid", nextOpenid[0])
  	}
  	uri.RawQuery = q.Encode()
  
  	response, err := util.HTTPGet(uri.String())
  	if err != nil {
  		return nil, err
  	}
  
  	userlist := new(OpenidList)
  	err = json.Unmarshal(response, userlist)
  	if err != nil {
  		return nil, err
  	}
  
  	return userlist, nil
  }
docs: // ListUserOpenIDs 返回用户列表