System.Net.WebClient vs. Proxy Authentication 407 error

Question

I\'m trying to figure out how to robustly handle proxy authentication errors (HTTP 407 status code) when using the System.Net.WebClient class.

In the field, we see many

Answer 1

Internet Explorer does not persistently cache/reuse proxy authentication credentials if the proxy auth uses BASIC or DIGEST. For Negotiate/NTLM, default credentials will be provided.

Hence, even though .NET inherits from IE settings, you won't get any "free" support for proxy authentication for Basic/Digest unless you happen to be running in IE; you'll need to prompt the user or provide a configuration screen.

Fiddler (www.fiddler2.com) has the "Request Proxy Authentication" option on the Rules menu that you can use to simulate this scenario for testing.