Git over HTTP; have flexible SASL authentication

Hello,

Git providers are inventing proprietary extensions to HTTP authentication for Git. It seems smarter to use SASL for this purpose, possibly allowing the client a choice and authentication ringback to the client's own domain.

I wrote an Internet Draft to allow just that, and we implemented it for Apache, Nginx and FireFox. I would love to learn if this list considers it a sensible extensions to Git. https://datatracker.ietf.org/doc/html/draft-vanrein-httpauth-sasl

If you think this is useful, it would be wonderful to mention that on the HTTP WorkGroup list as well, because they are now considering HTTP-SASL for adoption, a formal requisite to send "Authorization: SASL" headers. https://datatracker.ietf.org/wg/httpbis/about/

Thanks!

Rick van Rein InternetWide.org

Apache  :- https://gitlab.com/arpa2/apachemod/-/tree/master/arpa2_sasl
           https://gitlab.com/arpa2/apachemod/-/tree/master/arpa2_diasasl
Nginx   :- https://github.com/stef/ngx_http_auth_sasl_module
FireFox :- https://gitlab.com/arpa2/http_sasl_client

Rick van Rein <rick@openfortress.nl> writes:

To adopt things like this, the work to extend how to make extensible what is on WWW-Authenticate in the thread that contains this recent message https://lore.kernel.org/git/Y9LvFMzriAWUsS58@coredump.intra.peff.net/ may be relevant, perhaps?

On Fri, Jan 27, 2023 at 09:06:36AM -0800, Junio C Hamano wrote:

It's relevant, but I think there's a ways to go. That is just about passing WWW-Authenticate headers to helpers, which can then try to make sense of them. But Git would still only understand getting back a username/password from the helper, and passing it along to curl. And hopefully we'd do it all through curl's SASL support, and not invent our own handling.

I'm not sure what all that might might look like. I'm sure Matthew has probably thought about it, so I'll let him say something more intelligent. :)

-Peff

On 2023-02-01 03:24, Jeff King wrote:

These are the same thoughts I have on this. My patches only add support for the Git -> helper information flow, but don't make an attempt to change how helpers can change Git's (curl's) response or behaviour.

I had earlier iterations [1] of the patch that included the ability to change the auth type/headers that curl would respond with based on the helper's output.

For example:

protocol=https host=example.com password=<TOKEN> authtype=bearer

..would have Git configure curl to set CURLOPT_XOAUTH2_BEARER. However I pulled these patches to keep the scope of that series smaller. It's still my plan to reintroduce such a patch series in the future.

I'd imagine that Git could advertise to helpers that its version of curl supports SASL and a helper could enable or select this mechanism. Alternatively it could just be a Git config to enable it outright `credential.useSasl` or something. I haven't had chance to review SASL yet.

Thanks, Matthew

[1] https://lore.kernel.org/git/230118.86k01kxfr7.gmgdl@evledraar.gmail.com/T/#m37fffe327593ca4f7bf32a205b7ee1d1ecd1ed46

Hi Junio,

(Sorry for the late reply)

This framework tries to get away from just Basic / Digest auth, but if I read correctly, it still assumes a single authentication step, which greatly reduces the strength of authentication.

SASL assumes that the endpoints can hold state and progress through any challenge/response exchange, in multiple steps if needed. This is not trivial with stateless HTTP, but we fixed it with a "s2s" argument which can hold the (datestamped, signed, encrypted) state on the server side.

A few mechanisms that spring to mind as useful with Git over HTTP-SASL are

 - Kerberos / GSS-API, desirable for companies using its single sign-on
 _ FIDO, currently being added to SASL to benefit all protocols
 - OPAQUE, a very modern crypto, developed in IETF now
 - SXOVER-PLUS, our own work that calls back to a user's domain for login
	(so no server-stored credentials needed, only access control)

I'm curious if this would indeed be considered an improvement to Git.

Cheers,
 -Rick

Rick van Rein <rick@openfortress.nl> writes:

That's nice to know, and its applications below do look useful, at least to me.