docs: public int getUserGroup(String openId) {
          String url = WxEndpoint.get("url.group.user.get");
          String json = String.format("{\"openid\":\"%s\"}", openId);
          logger.debug("get user group: {}", json);
          String response = wxClient.post(url, json);
  
          Map<String, Object> map = JsonMapper.nonEmptyMapper().json2Map(response);
          if (map.containsKey("groupid")) {
              return (Integer) map.get("groupid");
          }
          return -1;
      }