微信公众平台开发中如何获得ACCESSTOKEN .Net

private string GetToken()
   {

     // 也可以这样写:
     //return GetPage("https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=你的appid&secret=你的secret", "");
    
     string res = "";
     HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create("https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential
&appid=你的appid&secret=你的secret");
 req.Method = "GET";
     using (WebResponse wr = req.GetResponse())
     {
       HttpWebResponse myResponse = (HttpWebResponse)req.GetResponse();


       StreamReader reader = new StreamReader(myResponse.GetResponseStream(), Encoding.UTF8);


       string content = reader.ReadToEnd();
  
       List<ACCESSTOKEN> myACCESSTOKEN = Json.JSONStringToList<ACCESSTOKEN>(content);
       res = myACCESSTOKEN[0].access_token;
 
     }


     return res;
   }
   public string GetPage(string posturl, string postData)
   {
     Stream outstream = null;
     Stream instream = null;
     StreamReader sr = null;
     HttpWebResponse response = null;
     HttpWebRequest request = null;
     Encoding encoding = Encoding.UTF8;
     byte[] data = encoding.GetBytes(postData);
     // 准备请求...
     try
     {
       // 设置参数
       request = WebRequest.Create(posturl) as HttpWebRequest;
       CookieContainer cookieContainer = new CookieContainer();
       request.CookieContainer = cookieContainer;
       request.AllowAutoRedirect = true;
       request.Method = "POST";
       request.ContentType = "application/x-www-form-urlencoded";
       request.ContentLength = data.Length;
       outstream = request.GetRequestStream();
       outstream.Write(data, 0, data.Length);
       outstream.Close();
       //发送请求并获取相应回应数据
       response = request.GetResponse() as HttpWebResponse;
       //直到request.GetResponse()程序才开始向目标网页发送Post请求
       instream = response.GetResponseStream();
       sr = new StreamReader(instream, encoding);
       //返回结果网页（html）代码
       string content = sr.ReadToEnd();
       string err = string.Empty;
       return content;
     }
     catch (Exception ex)
     {
       string err = ex.Message;
       Response.Write(err);
       return string.Empty;
     }
   }