Я пытаюсь сохранить куки в пост-запросе. Вот мой код:

        CookieContainer myCookieContainer = new CookieContainer();
        HttpWebRequest myHttpWebRequest = (HttpWebRequest)WebRequest.Create(url);
        myHttpWebRequest.ContentType = "application/x-www-form-urlencoded";
        myHttpWebRequest.UserAgent = userAgent;
        myHttpWebRequest.CookieContainer = myCookieContainer;
        myHttpWebRequest.Method = "POST";

        byte[] postdata = encoding.GetBytes(submitString);

        myHttpWebRequest.BeginGetRequestStream(async1 =>
        {
            using (Stream stream = myHttpWebRequest.EndGetRequestStream(async1))
                stream.Write(postdata, 0, postdata.Length);
            myHttpWebRequest.BeginGetResponse(async2 =>
            {
                HttpWebResponse rep = (HttpWebResponse)myHttpWebRequest.EndGetResponse(async2);
                CookieCollection cookies = rep.Cookies;
                using (Stream stream = rep.GetResponseStream())
                using (StreamReader sr = new StreamReader(stream))
                {
                    String content = sr.ReadToEnd();
                    if (pageDownloadedEventHandler != null)
                        pageDownloadedEventHandler(content);
                }
            }, null);
        }, null);

Всегда CookieContainer пуст. Как получить печенье?