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Asked: 2026-05-12T06:22:29+00:00

I’m trying to figure out how to robustly handle proxy authentication errors (HTTP 407

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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 users receiving a 407 proxy authentication
WebException, but I’m not sure what a good default strategy is. In .Net
2.0/3.5, the proxy authentication settings are supposed to be inherited from
the Internet Explorer system settings. Firefox, Opera and Chrome use these
same settings.

Here’s the basic code we are using:

using System.Net;

string url = "http://www.mysite.com";
WebClient webClient = new WebClient();
byte[] data = webClient.DownloadFile(url);

When this code fails, we open the user’s browser and send them to a help
page. From our web logs, we know these customers can successfully connect in
their browsers. Perhaps they are manually entering their proxy user name and
password before they get to our help page? We don’t know.

It seems that we could use WebClient.UseDefaultCredentials, but this
seems redundant if WebClient is using the system settings anyway.

Any help is appreciated.

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1 Answer

  1. Editorial Team

    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.

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