Re: [PATCH] http.c: shell command evaluation for extraheader

From: Colin Arnott <colin@urandom.co.uk>
To: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Cc: "git@vger.kernel.org" <git@vger.kernel.org>
Subject: Re: [PATCH] http.c: shell command evaluation for extraheader
Date: Tue, 06 Mar 2018 01:09:58 -0500	[thread overview]
Message-ID: <-mpHjLv0pGYld30rBagku1GYfPM2FqZQubWD4rHt2K_uijQg0ehMjeBnZgr4K77zc2E4HAlm3eqNtP7-lXzhR8o7udP0TdNHMJK7WRauzmk=@urandom.co.uk> (raw)
In-Reply-To: <nycvar.QRO.7.76.6.1803051437000.20700@ZVAVAG-6OXH6DA.rhebcr.pbec.zvpebfbsg.pbz>

Johannes,

On March 5, 2018 1:47 PM, Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:

> As the credential-helper is already intended for sensitive data, and as it
> already allows to interact with a helper, I would strongly assume that it
> would make more sense to try to extend that feature (instead of the simple
> extraHeader one).

To confirm you are suggesting that the credential struct, defined in credential.h, be extended to include a headers array, like so:

--- a/credential.h
+++ b/credential.h
@@ -15,6 +15,7 @@ struct credential {
        char *protocol;
        char *host;
        char *path;
+       char **headers
 };
 
 #define CREDENTIAL_INIT { STRING_LIST_INIT_DUP }

> This would also help alleviate all the quoting/dequoting issues involved
> with shell scripting.
> 
> Besides, the http.extraHeader feature was designed to accommodate all
> kinds of extra headers, not only authentication ones (and indeed, the
> authentication was only intended for use in build agents, where both
> environment and logging can be controlled rather tightly).

I realise that my examples are scoped for auth, but I can conceive of other mutating headers that are not explicitly authentication related, and could benefit from shell execution before fetch, pull, push actions.

> I also see that in your implementation, only the extraHeader value is
> evaluated, without any access to the rest of the metadata (such as URL,
> and optionally specified user).
>
> It would probably get a little more complicated than a shell script to
> write a credential-helper that will always be asked to generate an
> authentication, but I think even a moderate-level Perl script could be
> used for that, and it would know the URL and user for which the
> credentials are intended...

You are correct; the scope provided by http.<url>.* is enough to meet my use cases, however I agree the lack of access to metadata limits what can be done within in the context of the shell, and makes the case for a credential-helper implementation stronger. I think there is something to be said about the simplicity and user-friendliness of allowing shell scripts for semi-complex config options, but authentication is a task that should be handled well and centrally, thus extending the credential-api makes sense.

Without Wax,
Colin Arnott
