Authenticated HttpWebRequest with redirection, persisting credentials? - asp.net

Question

My ASP.NET 2.0 app creates a HTTPWebRequest to a site within a company's intranet, which uses NTLM authentication. The credentials passed are for a service account, which is authenticated on the domain successfully (the security log confirms this)
Some abbreviated code follows..
HttpWebRequest req = WebRequest.Create(queryUrl) as HttpWebRequest;
NetworkCredential cred = new NetworkCredential(username,
pwd, domain);
req.Credentials = cred;
HttpWebResponse response = req.GetResponse() as HttpWebResponse;
As part of the request, there are a couple of redirections (within the same domain) to the final response - which is handled OK on my dev machine (Windows 2k)
When this request is created from my deployment environment (Windows 2k3), I get a 401 Unauthorized error returned from the site, seemingly after the first redirect code is returned (301 Moved), and my request object attempts to follow the redirect.
So basically, does anyone know of any issues surrounding authenticated HttpWebRequests that follow redirections?
PS - The obvious workaround is to simply request the page redirected to - but I the admins in charge of the intranet site want to monitor my app's usage by redirecting me through a specific page.

Answer 1

For HttpWebRequest to reuse credentials across redirects you need to use a credential cache.
If you just assign a NetworkCredentials object it will only be used on the first request.
Here is an example:
HttpWebRequest req = WebRequest.Create(queryUrl) as HttpWebRequest;
NetworkCredential cred = new NetworkCredential(username, pwd, domain);
var cache = new CredentialCache {{queryUrl, "Ntlm", cred}};
req.Credentials = cache;
HttpWebResponse response = req.GetResponse() as HttpWebResponse;

Answer 2

It's going to depend on how your auth. scheme works. The Network credentials is only going to help for the NTLM part of if. I suspect that the site you are trying to access is using forms authentication also. If this is the case, when you log in you should get an auth cookie, you will need to include that in subsequent requests, e.g. after a redirect. I think the WebRequest object has a headers collection that you can use to hold the cookie. Might be a good idea to use fiddler or firebug to see what is coming across when you normally browse.

Answer 3

If you are using NTLM, This is the classic 2 hop problem. It works on your dev machine because the client and the server are on the same box and the credentials are passed at most once (to the redirect final target machine i'm guessing)
When you deploy to your prod environment, there are 3 machines involved. Client browser passes credentials to server1, then server1 tries to pass the credentials to server2 which is not allowed. One work around is to implement Kerberos authentication (a stricter protocol) which will allow server1 to pass credentials to server2