protected void Page_Load(object sender, EventArgs e)
        {
            try  //仅仅是第一次绑定微信时认证通过
            {
                string signature = Request["signature"].ToString();
                string timestamp = Request["timestamp"].ToString();
                string nonce = Request["nonce"].ToString();
                string echostr = Request["echostr"].ToString();  //随机数
                Response.Write(echostr);
            }
}

 public void ProcessRequest(HttpContext context)
        {
            string WeiXinToken = "1234";//要和你微信公众平台设置的保持一致

            string echoString = context.Request.QueryString["echoStr"];
            string signature = context.Request.QueryString["signature"];
            string timestamp = context.Request.QueryString["timestamp"];
            string nonce = context.Request.QueryString["nonce"];

            if (CheckSignature(WeiXinToken, signature, timestamp, nonce))
            {
                if (!string.IsNullOrEmpty(echoString))
                {
                    context.Response.Write(echoString);
                    context.Response.End();
                }
            }
        }

        /// <summary>
        /// 验证微信签名
        /// </summary>
        public static bool CheckSignature(string token, string signature, string timestamp, string nonce)
        {
            string[] ArrTmp = { token, timestamp, nonce };

            Array.Sort(ArrTmp);
            string tmpStr = string.Join("", ArrTmp);

            tmpStr = FormsAuthentication.HashPasswordForStoringInConfigFile(tmpStr, "SHA1");
            //tmpStr = Membership.CreateUser(tmpStr, "SHA1");
            tmpStr = tmpStr.ToLower();

            if (tmpStr == signature)
            {
                return true;
            }
            else
            {
                return false;
            }
        }