RE: [PATCH] http(s): automatically try NTLM authentication first

[David Turner <David.Turner@twosigma.com>]

> -----Original Message-----
> From: Junio C Hamano [mailto:jch2355@gmail.com] On Behalf Of Junio C
> Hamano
> Sent: Wednesday, February 22, 2017 3:20 PM
> To: David Turner <David.Turner@twosigma.com>
> Cc: git@vger.kernel.org; sandals@crustytoothpaste.net; Johannes Schindelin
> <johannes.schindelin@gmx.de>; Eric Sunshine
> <sunshine@sunshineco.com>; Jeff King <peff@peff.net>
> Subject: Re: [PATCH] http(s): automatically try NTLM authentication first
> 
> David Turner <dturner@twosigma.com> writes:
> 
> > From: Johannes Schindelin <johannes.schindelin@gmx.de>
> >
> > It is common in corporate setups to have permissions managed via a
> > domain account. That means that the user does not really have to log
> > in when accessing a central repository via https://, but that the
> > login credentials are used to authenticate with that repository.
> >
> > The common way to do that used to require empty credentials, i.e.
> > hitting Enter twice when being asked for user name and password, or by
> > using the very funny notation https://:@server/repository
> >
> > A recent commit (5275c3081c (http: http.emptyauth should allow empty
> > (not just NULL) usernames, 2016-10-04)) broke that usage, though, all
> > of a sudden requiring users to set http.emptyAuth = true.
> >
> > Which brings us to the bigger question why http.emptyAuth defaults to
> > false, to begin with.
> 
> This is a valid question, and and I do not see it explicitly asked in the thread:
> 
> https://public-
> inbox.org/git/CAPig+cSphEu3iRJrkdBA+BRhi9HnopLJnKOHVuGhUqavtV1RXg
> @mail.gmail.com/#t
> 
> even though there is a hint of it already there.
> 
> > It would be one thing if cURL would not let the user specify
> > credentials interactively after attempting NTLM authentication (i.e.
> > login credentials), but that is not the case.
> >
> > It would be another thing if attempting NTLM authentication was not
> > usually what users need to do when trying to authenticate via https://.
> > But that is also not the case.
> 
> Some other possible worries we may have had I can think of are:
> 
>  - With this enabled unconditionally, would we leak some information?

I think "NTLM" is actually a misnomer here (I just copied Johannes's 
commit message). The mechanism is actually SPNEGO, if I understand this 
correctly. It seems to me that this is probably secure, since it is apparently
widely implemented in browsers.

>  - With this enabled unconditionally, would we always incur an extra
>    roundtrip for people who are not running NTLM at all?
>
> I do not think the former is the case, but what would I know (adding a few
> people involved in the original thread to CC: ;-)

Always, no.  For failed authentication (or authorization), apparently, yes.  
I tested this by  setting the variable to false and then true, and trying to 
Push to a github repository which I didn't have write access to, with 
both an empty username (https://@:github.com/...) and no username 
(http://github.com/...).   I ran this under GIT_CURL_VERBOSE=1 and
I saw two 401 responses in the "http.emptyauth=true" case and one
in the false case.  I also tried with a repo that I did have access to (first
configuring the necessary tokens for HTTPS push access), and saw two
401 responses in *both* cases.