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

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Colin,

On Tue, 6 Mar 2018, Colin Arnott wrote:

> 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 }

I think that was what I had in mind, yes.

> > 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 can conceive of yet another use case that would benefit from shell
execution in these scenarios: attacks. That is why I am extremely hesitant
to go that route.

But then, I am not the maintainer of Git. If you can convince him, you're
good to go.

> > 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.

Yes, I agree.

Ciao,
Johannes