微信授权第三方登陆

 public void ProcessRequest(HttpContext context)
        {
            var appid = ConfigurationManager.AppSettings["WeiXinAppId"] ?? string.Empty;
            var secret = ConfigurationManager.AppSettings["WeiXinSecret"]??string.Empty;
            var weburl = ConfigurationManager.AppSettings["WebUrl"]??"您的网址";
            string errorCode = "微信登录过期,请重新登录！";
            var code = context.Request.QueryString["Code"];
            if (string.IsNullOrEmpty(code))
            { 
                var url =
                    string.Format(
                        "https://open.weixin.qq.com/connect/qrconnect?appid={0}&redirect_uri={1}?referer_key={2}&response_type=code&scope=snsapi_login", appid,StringFilter.UrlEncode(string.Format("{0}/Api/Oauth/weixin/login/UserAuth.ashx", weburl)),secret);
                context.Response.Redirect(url);
            }
            else
            {
                var client = new System.Net.WebClient();
                client.Encoding = System.Text.Encoding.UTF8;
                var url = string.Format("https://api.weixin.qq.com/sns/oauth2/access_token?appid={0}&secret={1}&code={2}&grant_type=authorization_code", appid, secret, code);
                var data = client.DownloadString(url);

                var serializer = new JavaScriptSerializer();
                var obj = serializer.Deserialize<Dictionary<string, string>>(data);
                string accessToken;
                if (!obj.TryGetValue("access_token", out accessToken))
                    return;

                var opentid = obj["openid"];
                url = string.Format("https://api.weixin.qq.com/sns/userinfo?access_token={0}&openid={1}&lang=zh_CN", accessToken, opentid);
                data = client.DownloadString(url);