public class OAuth
    {
        public static HttpClient httpClient = new HttpClient();
        public static string GetAuthorizeUrl(string appId, string redirectUrl, string state= "state", string scope = "snsapi_base", string responseType = "code")
        {
            if (!string.IsNullOrEmpty(redirectUrl))
            {
                redirectUrl = HttpUtility.UrlEncode(redirectUrl, System.Text.Encoding.UTF8);
            }
            else
            {
                redirectUrl = null;
            }
            object[] args = new object[] { appId, redirectUrl, responseType, scope, state };
            return string.Format("https://open.weixin.qq.com/connect/oauth2/authorize?appid={0}&redirect_uri={1}&response_type={2}&scope={3}&state={4}#wechat_redirect", args);
        }

        public static string GetOpenIdUrl(string appId, string secret, string code, string grantType = "authorization_code")
        {
            object[] args = new object[] { appId, secret, code, grantType };
            string requestUri = string.Format("https://api.weixin.qq.com/sns/oauth2/access_token?appid={0}&secret={1}&code={2}&grant_type={3}", args);
            return requestUri;
        }

        /// <summary>
        /// 获取openid
        /// </summary>
        /// <param name="appId"></param>
        /// <param name="secret"></param>
        /// <param name="code"></param>
        /// <param name="grantType"></param>
        /// <returns></returns>
        public static string GetOpenid(string appId, string secret, string code, string grantType = "authorization_code")
        {
            string requestUri = GetOpenIdUrl(appId, secret, code, grantType);
            var responseStr = httpClient.GetAsync(requestUri).Result.Content.ReadAsStringAsync().Result;
            var obj = JsonConvert.DeserializeObject<Dictionary<string, string>>(responseStr);
            string openid = string.Empty;
            if (!obj.TryGetValue("openid", out openid))
            {
                Log.Info($"获取openid失败appId={appId}，secret={secret}，code={code}");
            }
            return openid;
        }
    }

/// <summary>
       /// 获取微信openid
       /// </summary>
       /// <param name="code"></param>
       /// <returns></returns>
       [HttpGet]
        public IActionResult GetWxOpenid(string code)
        {
            WxPayConfig wxPayConfig = new WxPayConfig();
            //首先构造微信请求授权url，重定向到该url中，其中redirectUrl是回调地址，必须保证该地址在公网上能访问，本例子构造的是返回到本控制器的方法。
            //若是从微信授权返回进入该方法，则会带上一个参数，code就不为空，若code为空则跳转微信授权
            if (string.IsNullOrEmpty(code))
            {
                var redirectUrl = OAuth.GetAuthorizeUrl(wxPayConfig.appid, "回调地址到公网本Action");
                return Redirect(redirectUrl);
            }
            else
            {
                //根据code和微信参数得到openid
                var openId = OAuth.GetOpenid(wxPayConfig.appid, wxPayConfig.appSecret, code);
                //业务处理
                
            }
            return View();
        }