public partial class wxapi : System.Web.UI.Page
    {
        const string _token = "在微信公众测试号后台写的那个Token";
        private const string _myOpenid = "你自己微信公众测试号的appID";
        string postStr = "";
        protected void Page_Load(object sender, EventArgs e)
        {
            //***********  验证成为开发者之后将此代码注释 *************//
            string httpMethod = Request.HttpMethod.ToLower();
            if (httpMethod == "post")
            {
                //第一次验证的时候开启
                FirstValid();
            }
            else
            {
                Valid();  //如果不是post请求就去做开发者验证
            }
        }

        /// <summary>
        /// 验证成为开发者
        /// </summary>
        private void Valid()
        {
            string echoStr = Request.QueryString["echoStr"].ToString();
            if (CheckSignature())
            {
                if (!string.IsNullOrEmpty(echoStr))
                {
                    Response.Write(echoStr);
                    Response.End();
                }
            }
        }

        /// <summary>
        /// 验证微信签名
        /// </summary>
        /// * 将token、timestamp、nonce三个参数进行字典序排序
        /// * 将三个参数字符串拼接成一个字符串进行sha1加密
        /// * 开发者获得加密后的字符串可与signature对比，标识该请求来源于微信。
        /// <returns></returns>
        private bool CheckSignature()
        {
            string signature = Request.QueryString["signature"].ToString();
            string timestamp = Request.QueryString["timestamp"].ToString();
            string nonce = Request.QueryString["nonce"].ToString();
            string[] ArrTmp = { _token, timestamp, nonce };
            Array.Sort(ArrTmp);     //字典排序
            string tmpStr = string.Join("", ArrTmp);
            tmpStr = FormsAuthentication.HashPasswordForStoringInConfigFile(tmpStr, "SHA1");
            tmpStr = tmpStr.ToLower();
            if (tmpStr == signature)
            {
                return true;
            }
            else
            {
                return false;
            }
        }

        /// <summary>
        /// 第一次验证配置
        /// </summary>
        private void FirstValid()
        {
            Stream s = System.Web.HttpContext.Current.Request.InputStream;
            byte[] b = new byte[s.Length];
            s.Read(b, 0, (int)s.Length);
            postStr = Encoding.UTF8.GetString(b);
            if (!string.IsNullOrEmpty(postStr))
            {
                ResponseMsg(postStr);
            }
        }

        /// <summary>
        /// 返回信息结果(微信信息返回)
        /// </summary>
        /// <param name="weixinXML"></param>
        private void ResponseMsg(string weixinXML)
        {
            //回复消息的部分:你的代码写在这里
        }
}