【微信公众号】验证用户OpenID是否关注某个公众号

1、获取OpenID

　　　　 #region 获取微信支付的OpenId

        /// <summary>
        /// 获取微信支付的OpenId
        /// </summary>
        /// <returns></returns>
        public string GetPayOpenID()
        {
            try
            {
　　　　　　　　　string code = Request.QueryString["code"];
                if (string.IsNullOrEmpty(code))
                {
                    string url = "https://open.weixin.qq.com/connect/oauth2/authorize?appid=" + Constant.WX_PAY_APPID +
                        "&redirect_uri=" + HttpUtility.UrlEncode(Request.Url.ToString()) +
                        "&response_type=code&scope=snsapi_base&state=123#wechat_redirect";
                }
                else
                {
                    string url = "https://api.weixin.qq.com/sns/oauth2/access_token?appid=" + Constant.WX_PAY_APPID +
                        "&secret=" + Constant.WX_PAY_APPSECRET + "&code=" + code + "&grant_type=authorization_code";
　　　　　　　　　　　 string jsonResult = new System.Net.Http.HttpClient().GetStringAsync(url).Result;
                    JToken jtoken = JToken.Parse(jsonResult);
                    string openid = jtoken.Value<string>("openid");
                    return openid;
                }
            }
            catch (Exception ex)
            {
            }
            return "";
        }

        #endregion

2、获取Token

https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=***&secret=***

响应结果：

{
    "access_token":"O3PwqnKoiiYmsHeAh8viWLQyhGRrGU6RT9o53pvlmhIBWQnTXeZDSkYNw6YufzIDUspzQguvxtmLXtAWmQd2NmurXKa4N4PsbwG7RvI25pqzSC3-cLl50iqSW5VaZ4xmGXQgAFAJAT",
    "expires_in":
}

3、使用Token和OpenID获取用户信息

https://api.weixin.qq.com/cgi-bin/user/info?access_token=***&openid=***&lang=zh_CN

响应结果：

{
    "subscribe":,
    "openid":"oeQDZt0n4VCZ70wy***",
    "nickname":"背上***旅行",
    "sex":,
    "language":"zh_CN",
    "city":"昌平",
    "province":"北京",
    "country":"中国",
    "headimgurl":"http://wx.qlogo.cn/mmopen/kBwGJuwqK9**********************ibVUEpgFE90LH3b3uj7AYRjZP/0",
    "subscribe_time":,
    "unionid":"oGCG8t5**********jPQTPw",
    "remark":"",
    "groupid":,
    "tagid_list":[

    ]
}

根据接口返回的subscribe字段判断是否关注公众号
1=关注；0=未关注；

subscribe：用户是否订阅该公众号标识，值为0时，代表此用户没有关注该公众号，拉取不到其余信息。

没有关注的情况下，显示这个。。。

今天又遇到这个问题了

{"subscribe":0,"openid":"oeQDZtzPrIYwOPXdzgKmd0gYPG44","unionid":"oGCG8tzd2NwsOYAeWAZMwV9rMmPU","tagid_list":[]}