Set credentials to a web request

Hi,
I'm trying to run an automated test (using NTime tool) on a web application
(windows authentication). All calls in this web app are intercepted by a
custom httpModule. I'm setting credentials to the web request so that the
authentication passes but this doesn't seem to work:

NetworkCredential obj = new NetworkCredential();
obj.UserName = @"domain\username";
obj.Password = "test123";
HttpWebRequest myRequest = (HttpWebRequest)
HttpWebRequest.Create("https://testsite.com/testapp/samplepage.aspx");
myRequest.Credentials = obj;

Please suggest the solution.
Thanks