#region 1.0验证消息的真实性 - private void ValidateUrl()
private void ValidateUrl()
{
    #region 获取微信服务器Get发送过来的四个参数
    //开发者提交信息后，微信服务器将发送GET请求到填写的服务器地址URL上，GET请求携带四个参数：
    HttpContext context = HttpContext.Current;
    //微信加密签名，signature结合了开发者填写的token参数和请求中的timestamp参数、nonce参数。
    string signature = context.Request.QueryString["signature"];
    //时间戳
    string timestamp = context.Request.QueryString["timestamp"];
    //随机数
    string nonce = context.Request.QueryString["nonce"];
    //随机字符串
    string echostr = context.Request.QueryString["echostr"];
    #endregion

    #region 加密/校验来自微信服务器的请求
    string token = "Kim2015";//必须跟公共账号上的一致
    //1. 将token、timestamp、nonce三个参数进行字典序排序
    string[] temp1 = { token, timestamp, nonce };
    Array.Sort(temp1);

    //2. 将三个参数字符串拼接成一个字符串进行sha1加密
    string temp2 = string.Join("", temp1);
    string temp3 = FormsAuthentication.HashPasswordForStoringInConfigFile(temp2,
        FormsAuthPasswordFormat.SHA1.ToString());
    //3. 若确认此次GET请求来自微信服务器，请原样返回echostr参数内容
    if (temp3.ToLower().Equals(signature))
    {
        context.Response.Write(echostr);
    }
    #endregion

#region 2.0接收并处理文本信息 - private void HandleTextMsg()
private void HandleTextMsg()
{
    #region 接收微信服务器POST发送过来的xml数据包
    /*
     <xml>
    <ToUserName><![CDATA[toUser]]></ToUserName>
    <FromUserName><![CDATA[fromUser]]></FromUserName> 
     <CreateTime>1348831860</CreateTime>
    <MsgType><![CDATA[text]]></MsgType>
    <Content><![CDATA[this is a test]]></Content>
    <MsgId>1234567890123456</MsgId>
     </xml>
     */
    HttpContext context = HttpContext.Current;
    //接收xml数据包
    Stream xmlStream = context.Request.InputStream;
    //构造xml对象
    XmlDocument doc = new XmlDocument();
    doc.Load(xmlStream);
    //获取根节点
    XmlElement rootElement = doc.DocumentElement;
    //解析xml数据
    string toUserName = rootElement.SelectSingleNode("ToUserName").InnerText;
    string fromUserName = rootElement.SelectSingleNode("FromUserName").InnerText;
    string createTime = rootElement.SelectSingleNode("CreateTime").InnerText;
    string msgType = rootElement.SelectSingleNode("MsgType").InnerText;
    string content = rootElement.SelectSingleNode("Content").InnerText;
    string msgId = rootElement.SelectSingleNode("MsgId").InnerText;
    
    #endregion

    #region 解析xml数据包，并按照一定格式返回
    /*
     <xml>
    <ToUserName><![CDATA[toUser]]></ToUserName>
    <FromUserName><![CDATA[fromUser]]></FromUserName>
    <CreateTime>12345678</CreateTime>
    <MsgType><![CDATA[text]]></MsgType>
    <Content><![CDATA[你好]]></Content>
    </xml>
     */

    string xmlMsg = "<xml>" +
                    "<ToUserName><![CDATA[" + fromUserName + "]]></ToUserName>" +
                    "<FromUserName><![CDATA[" + toUserName + "]]></FromUserName>" +
                    "<CreateTime>" + GetCreateTime() + "</CreateTime>" +
                    "<MsgType><![CDATA[text]]></MsgType>" +
                    "<Content><![CDATA[“很高兴认识你”]]></Content>" +
                    "</xml>";
    context.Response.Write(xmlMsg); 
    #endregion
}
#endregion

public void ProcessRequest(HttpContext context)
{
    
    if (context.Request.HttpMethod.ToLower().Equals("get"))
    {
       context.Response.Write(msg);
        //校验
        ValidateUrl();
    }
    else
    {
        //当普通微信用户向公众账号发消息时，微信服务器将POST消息的XML数据包到开发者填写的URL上
        HandleTextMsg();
    }
}