尝试登录HttpWebRequest和HttpWebResponse c#WPF

我正在尝试登录此网站：

但是最后，他仍然没有登录，我正在打开页面，捕获会话并尝试登录，为什么最后，不工作登录

看看我的代码：

string url = "http://svp.correios.com.br/core/seguranca/entrar.php";
        //request page to login
        HttpWebRequest request01 = (HttpWebRequest)WebRequest.Create(url);
        request01.CookieContainer = _cookies;
        request01.ContentType = "application/x-www-form-urlencoded";
        //load page
        HttpWebResponse return01 = (HttpWebResponse)request01.GetResponse();
        Stream dataStream = return01.GetResponseStream();
        StreamReader reader = new StreamReader(dataStream, Encoding.GetEncoding("ISO-8859-1"));


        //get section
        string responseFromServer = reader.ReadToEnd();
        String[] rastreamentoCompleto = Regex.Split(responseFromServer, "<section id=\"geral\">\n\t<form id=\"fm1\" action=\"");
        String[] retiraFim = Regex.Split(rastreamentoCompleto[1], "\" method=\"post\">\n    <div id");
        string keySection = retiraFim[0];

        //try login
        HttpWebRequest request02 = (HttpWebRequest)WebRequest.Create("https://apps.correios.com.br" + keySection);
        request02.CookieContainer = _cookies;
        request02.Method = "POST";
        string postData = "username="+ user + "&password="+ password;
        byte[] byteArray = Encoding.UTF8.GetBytes(postData);
        request02.ContentType = "application/x-www-form-urlencoded";
        request02.ContentLength = byteArray.Length;
        dataStream = request02.GetRequestStream();
        dataStream.Write(byteArray, 0, byteArray.Length);
        dataStream.Close();




        //check if Logged
        HttpWebResponse return02 = (HttpWebResponse)request02.GetResponse();
        dataStream = return02.GetResponseStream();
        reader = new StreamReader(dataStream, Encoding.GetEncoding("ISO-8859-1"));
        responseFromServer = reader.ReadToEnd();

stringurl=”http://svp.correios.com.br/core/seguranca/entrar.php";
//请求页面登录
HttpWebRequest01=（HttpWebRequest）WebRequest.Create（url）；
request01.CookieContainer=\u cookies；
request01.ContentType=“application/x-www-form-urlencoded”；
//加载页
HttpWebResponse return01=（HttpWebResponse）request01.GetResponse（）；
Stream dataStream=return01.GetResponseStream（）；
StreamReader=新的StreamReader（dataStream，Encoding.GetEncoding（“ISO-8859-1”）；
//获取部分
字符串responseFromServer=reader.ReadToEnd（）；
String[]rastreamentoCompleto=Regex.Split（responseFromServer，“\n\t\n您必须解析所有
元素（该页面隐藏了
元素；这些元素需要与其他元素一起发布URL编码）。它没有
\uu视图状态
（但它可以，因此您也应该对此进行解析）。如果用户名或密码字段包含电子邮件地址，请不要对该字段进行URL编码。我如何才能做到这一点？