Авторизация на сайте с https

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Net;
using System.IO;
using System.Security.Cryptography.X509Certificates;
 
namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1(){
            InitializeComponent();
        }
 
        private void button1_Click(object sender, EventArgs e){
            ServicePointManager.CertificatePolicy = new AcceptAllCertificatePolicy();
            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create("https://serviceguide.megafonvolga.ru:443");
            NetworkCredential nwCredential = new NetworkCredential("tbUser", "tbPass");
            request.Credentials = nwCredential;
            X509Certificate cer = X509Certificate.CreateFromCertFile("D:\\cacert.cer");
            request.ClientCertificates.Add(cer);
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            StreamReader reader = new StreamReader(response.GetResponseStream(),Encoding.ASCII);
            string s = reader.ReadToEnd();
            webBrowser1.DocumentText=s;
            response.Close();
            reader.Close(); 
        }
        internal class AcceptAllCertificatePolicy : ICertificatePolicy
        {
            public AcceptAllCertificatePolicy(){}
            public bool CheckValidationResult(ServicePoint sPoint, X509Certificate cert,
            WebRequest wRequest, int certProb){
                return true;
            }
        }
    }
}

NetworkCredential nwCredential = new NetworkCredential("tbUser", "tbPass");
            request.Credentials = nwCredential;

var bytes = System.Encoding.UTF8.GetBytes("str");
request.Headers["Content-Length"] = bytes.Length;
request.Headers["Content-Type"] = "application/x-www-form-urlencoded; charset=utf-8"
request.OpenRequestStream().Write(bytes, 0, bytes.Length);
var response = request.GetResponse()