Re: Git 2.23.0-rc0 HTTP authentication failure - error message change

[Jeff King <peff@peff.net>]

On Wed, May 19, 2021 at 12:12:52AM +0000, brian m. carlson wrote:

> > But imagine we didn't get a username/password in the URL. The first
> > request will return REAUTH because of this moved code path (just as it
> > would have before, because http.auth.{username,password} are not set).
> > And then we'll get a credential from the user or from a helper and try
> > again. But this time, if we fail, we'll return HTTP_REAUTH again! We
> > never hit the "if (http_auth.username && http_auth.password)" check at
> > all. And hence we never return HTTP_NOAUTH (which gives us the more
> > useful "authentication failed" message), nor the credential_reject()
> > line (which informs helpers to stop caching a known-bad password).
> 
> I think what we'd want to do in this case is to only call HTTP_REAUTH if
> we actually cleared CURLAUTH_GSSNEGOTIATE.  Maybe something like this:
> [...]

Yeah, that was my instinct, too, but...

> > I suspect we could hack around it by pessimistically guessing that
> > GSSNEGOTIATE was the problem. But I'm worried that making that work
> > would require up to three requests (one to find out we need auth, one to
> > remove the GSSNEGOTIATE bit, and one to retry with a username/password).
> > That seems like punishing people with servers that don't even care about
> > Negotiate for no reason.
> 
> I think my proposal above does that, but I'm not sure.  If Negotiate
> wasn't set, we won't need to make a third request, since we'll have
> known the supported mechanisms as part of the original 401.  If they do
> support both, then three requests will be required if they have to fall
> back to Basic auth, but then they're only paying the price for the
> environment they have.
> 
> If we aren't already reading the supported mechanisms out of the initial
> 401, then we'll need the third request, but that would be silly and we
> should just avoid doing that.

Yeah, I was worried that just clearing the bit results in the extra
round-trip. I think we do clear bits based on what the other side showed
us. That's the:

  http_auth_methods &= results->auth_avail;

in the code being discussed. But it seems like we'd want to do that as
part of setting the "used negotiate" flag in your sample patch. I.e.,:

  if (http_auth_methods & results->auth_avail & CURLAUTH_GSSNEGOTIATE)
          used_negotiate = 1;

But it's entirely possible I don't understand the subtleties around
unsetting GSSNEGOTIATE in the first place (it's not something I've ever
used myself).

> > So perhaps somebody can come up with something clever, but I suspect we
> > may need to just revert this for the v2.32 release, and re-break the
> > case that 1b0d9545bb8 was trying to solve.
> 
> Yeah, I think this is the right solution for the problem until somebody
> with a suitable mixed auth environment shows up and can test.  Your
> patches seemed reasonable and, as always, well explained.

Thanks for taking a look!

-Peff