How do I determine (elegantly) if proxy authentication is required in C# winforms app

Question

My use case is this, I want to call out to a webservice and if I am behind a proxy server that requires authentication I want to just use the default credentials...

Answer 1

It was only after I had first deployed my app that I realised some users were behind firewalls... off to work to test it. Rather than do a test for a '407 authentication required' I just do the same Proxy setup whether it might be needed or not...

System.Net.HttpWebRequest req = (System.Net.HttpWebRequest)System.Net.WebRequest.Create(uri.AbsoluteUri);
//HACK: add proxy
IWebProxy proxy = WebRequest.GetSystemWebProxy();
proxy.Credentials = System.Net.CredentialCache.DefaultCredentials;
req.Proxy = proxy;
req.PreAuthenticate = true;
//HACK: end add proxy
req.AllowAutoRedirect = true;
req.MaximumAutomaticRedirections = 3;
req.UserAgent = "Mozilla/6.0 (MSIE 6.0; Windows NT 5.1; DeepZoomPublisher.com)";
req.KeepAlive = true;
req.Timeout = 3 * 1000; // 3 seconds

I'm not sure what the relative advantages/disadvantages are (try{}catch{} without proxy first, versus just using the above), but this code now seems to work for me both at work (authenticating proxy) and at home (none).