If a proxy server requires authorization it returns an HTTP 407 (Proxy Authentication Required)

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Asked: May 21, 20262026-05-21T03:30:12+00:00 2026-05-21T03:30:12+00:00

If a proxy server requires authorization it returns an HTTP 407 (Proxy Authentication Required)

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If a proxy server requires authorization it returns an HTTP 407 (“Proxy Authentication Required”) status code.

However, what happens if a proxy server is provided authorization which is invalid? Does it return another HTTP 407 or an HTTP 401 (“Unauthorized”) or …? (A use-case might be where System.Net.WebClient from .NET uses the “default proxy credentials” which happen to be invalid.)

I wouldn’t mind some “steps to try it out myself”, but my HTTP-foo is weak and I have no such proxy server myself (so it’s more of a hypothetical question for me at this point). I have skimmed through RFC 2616 (including “14.34 Proxy-Authorization”) but I was not able to glean anything — very possibly an oversight on my part — and references to the applicable sections describing the behavior are also very much appreciated.