Re: Git + mod_auth_kerb

["brian m. carlson" <sandals@crustytoothpaste.net>]

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On Mon, Jul 21, 2014 at 05:06:50PM -0400, Jean-Francois Bouchard wrote:
> Hello,
> 
> We are currently working on a single sign on setup for our git install. We are
> using git 2.0.2 (ubuntu) plus apache/2.2.22 mod_auth_kerb on the
> server side. Here some scenario we are trying to accomplish :
> 
> -Without Kerberos ticket stored.
> Git ask for username/password.
> Result = Authentication failed
> 
> -Kerberos ticket in store and BAD password :
> Git ask for username/password.
> Result = Authentication failed
> 
> -Kerberos ticket in Store entering good password :
> Git ask for username/password.
> Result = Authentication failed on some host, other works
> 
> -Kerberos ticket in Store and embedding the username in the URI (aka
> https://username@repo)
> Git don't ask for anything or ask for password
> Result = Works on some host, other request the password. (Will fail if
> the kerberos ticket not in store)

So git uses libcurl with CURLAUTH_ANY.  In order for authentication to
work with libcurl, you have to supply a username.  If you specify it in
the URL, the libcurl realizes that it can use Kerberos, and goes on its
merry way.

If you don't specify the username in the URL, git notices that
authentication has failed, and asks the credential store for a username
and password.  git does not know that a password is not needed, so the
credential subsystem prompts for one anyway.

I have mod_auth_kerb set up against Apache 2.4.9 at the moment, although
I've used 2.2 before.  I always use a username in the URL, and if I get
prompted for the password, I just Ctrl-C out and run kinit before
pushing again.

I don't have mod_auth_kerb set up to fall back to basic auth, but if you
do, using a username and password should work properly.  You can use
set the environment variable GIT_CURL_VERBOSE to 1 to see more
information about what's actually going over the wire.

> This is a very strange behaviour. It seems to be cause by the way
> libcurl and git interact and the way the authentication goes
> (Negociate first, then basic auth). I have tried to use the helper to
> store invalid authentication information. With not much success.

libcurl will always prefer something (anything) over basic auth, since
basic auth is completely insecure unless you're using HTTPS.

-- 
brian m. carlson / brian with sandals: Houston, Texas, US
+1 832 623 2791 | http://www.crustytoothpaste.net/~bmc | My opinion only
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