I am trying to get the header \"Set-Cookie\" or access the cookie container, but the Set-Cookie header is not available. The cookie is in the response header, but it\'s not
Try explicitly passing a new CookieContainer:
CookieContainer container = new CookieContainer();
container.Add(new Uri("http://yoursite"), new Cookie("name", "value"));
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://yoursite");
request.CookieContainer = container;
request.BeginGetResponse(new AsyncCallback(GetData), request);