[Help] html form login in C#

        string formUrl = "freerainbowtablesdotcom"; 
            string formParams = string.Format("username={0}&password={1}&login=1","om3g4","MYPASS");
            string cookieHeader;
            string pageSource;

            WebRequest req = WebRequest.Create(formUrl);
            req.ContentType = "application/x-www-form-urlencoded";
            req.Method = "POST";
            byte[] bytes = Encoding.ASCII.GetBytes(formParams);
            req.ContentLength = bytes.Length;
            using (Stream os = req.GetRequestStream())
            {
                os.Write(bytes, 0, bytes.Length);
            }
            WebResponse resp = req.GetResponse();

            cookieHeader = resp.Headers["Set-cookie"];
           
            string getUrl = "freerainbowtablesdotcom";
            WebRequest getRequest = WebRequest.Create(getUrl);
            getRequest.Headers.Add("Cookie", cookieHeader);
            WebResponse getResponse = getRequest.GetResponse();
            using (StreamReader sr = new StreamReader(getResponse.GetResponseStream()))
            {
                pageSource = sr.ReadToEnd();
            }