How to send a login and password to the service via https?

I am trying to access the web service from getting a site http://zakupki.gov.ru I tried it this way, but it does not work.

webRequest = (HttpWebRequest)WebRequest.Create(uri); webRequest.Method = "POST"; webRequest.ProtocolVersion = HttpVersion.Version10; webRequest.KeepAlive = false; System.Net.Cache.RequestCachePolicy cashePol = new System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.NoCacheNoStore); webRequest.CachePolicy = cashePol; var credentials = new NetworkCredential("qwerty", "qwerty"); webRequest.Credentials = credentials; //2. Ввести данные к отправке и ковертировать их в массив байтов encodingUTF8 = System.Text.Encoding.UTF8; byteArray = encodingUTF8.GetBytes(postData);