I am logging into a page using HttpWebRequest and getting some information. I then use that information to create a new HttpWebRequest to get some more information. I do not
Add a CookieContainer to each request before you send it. Add the cookies you get from the first response to the second request. Assuming they use cookies for authentication, this should authenticate the second request.
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(urlWithParameters);
request.CookieContainer = new CookieContainer();
HttpWebResponse response = (HttpWebResponse) request.GetResponse();
var cookies = new CookieContainer();
cookies.Add( response.Cookies );
request = (HttpWebRequest)WebRequest.Create(secondUrlWithParameters);
request.CookieContainer = cookies;
...