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

We solved that problem by adding a config dialog which alows the user to choose "use proxy". If this setting is done we use these parameter (address, credentials...). If not - we assume that a connection can be made without any manual interaction. In the case of an error we do: a.) try again using default credentials b.) popup an information that a setting in config could help...

If proxy authentication is done via "default credentials" (Windows user) IE also reacts to an auth error and sends default credentials in this case. If this does not work it opens a credentials dialog. I'm not sure if all browsers handle this that way - but you can simply give it a try using fiddler, so you can see what's going on.