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();

        }