public void DoIT()
{
try
        {

            HttpWebRequest webRequest = WebRequest.Create(LOGIN_URL) as HttpWebRequest;
            StreamReader responseReader = new StreamReader(
                  webRequest.GetResponse().GetResponseStream()
               );
            string responseData = responseReader.ReadToEnd();
            responseReader.Close();

            // extract the viewstate value and build out POST data
            string viewState = ExtractViewState(responseData);
            string EventValidation = ExtractEventValidation(responseData);
            string viewstategen = ExtractViewStateGen(responseData);

            NameValueCollection outgoingQueryString = HttpUtility.ParseQueryString(String.Empty);
            outgoingQueryString.Add("__VIEWSTATE", viewState);
           outgoingQueryString.Add("__EVENTVALIDATION", EventValidation);
               outgoingQueryString.Add("__VIEWSTATEGENERATOR", viewstategen);
            outgoingQueryString.Add("__EVENTTARGET", string.Empty);
            outgoingQueryString.Add("__EVENTARGUMENT", string.Empty);

            outgoingQueryString.Add("Login1$UserName", "TestUser");
            outgoingQueryString.Add("Login1$Password", "TestPass");
            outgoingQueryString.Add("Login1$SiteDDL", "TestSite");
            outgoingQueryString.Add("ShowHospreferral", "true");


            outgoingQueryString.Add("Login1$LoginButton", "Login");

            var data = Encoding.ASCII.GetBytes(outgoingQueryString.ToString());
        string postData =
               String.Format(
                "__VIEWSTATE={0}& __EVENTVALIDATION={1}&__EVENTTARGET={2}&__EVENTARGUMENT={3}&__VIEWSTATEGENERATOR={4}&Login1$UserName={5}&Login1$Password={6}&Login1$SiteDDL={6}&ShowHospreferral={7}&Login1$LoginButton={8}",
          viewState ,EventValidation, HttpUtility.UrlEncodeUnicode(string.Empty), HttpUtility.UrlEncodeUnicode(string.Empty), viewstategen , "Dougie", "Cardiology1", "T101H", HttpUtility.UrlEncodeUnicode("true"),  "Login"
              );

            // have a cookie container ready to receive the forms auth cookie
            CookieContainer cookies = new CookieContainer();

            // now post to the login form
            webRequest = WebRequest.Create(LOGIN_URL) as HttpWebRequest;
            webRequest.Method = "POST";
            webRequest.ContentType = "application/x-www-form-urlencoded";
            webRequest.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3";
            webRequest.Headers.Set("Accept-Language", "en-GB,en-US;q=0.9,en;q=0.8");
            webRequest.Headers.Set("Accept-Encoding", "gzip, deflate, br");
            webRequest.Referer = LOGIN_URL;
            webRequest.UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36";
            webRequest.CookieContainer = cookies;

            // write the form values into the request message




            StreamWriter requestWriter = new StreamWriter(webRequest.GetRequestStream());
         requestWriter.Write(postData);
           requestWriter.Close();

            // we don't need the contents of the response, just the cookie it issues
            webRequest.GetResponse().Close();

            // now we can send out cookie along with a request for the protected page
            webRequest = WebRequest.Create(SECRET_PAGE_URL) as HttpWebRequest;
            webRequest.CookieContainer = cookies;
            responseReader = new StreamReader(webRequest.GetResponse().GetResponseStream());

            // and read the response
            responseData = responseReader.ReadToEnd();
            responseReader.Close();

            textBox1.Text = responseData;
        }
        catch (WebException webex)
        {
            WebResponse errResp = webex.Response;
            using (Stream respStream = errResp.GetResponseStream())
            {
                StreamReader reader = new StreamReader(respStream);
                textBox1.Text = reader.ReadToEnd();
            }
        }
    catch (Exception ex)
        { textBox1.Text = ex.Message; }
    }