Implement impersonation login using C#

i want to request a website in my application.
Authentication required for this website when i request it via IE.
i have the id and pw. how can i request it via code?

Authentication 

the login area is not a form build using html. it is a windows popup Authentication window.

string authenticationUrl = @"https://xxx"; // it'use https, not sure if this impact anything.
            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(authenticationUrl);
            req.Credentials = new NetworkCredential("id", "pw");
            using (WebResponse wr = req.GetResponse())
            {
                //error here: Authentication failed because the remote party has closed the transport stream.
            }