Re: [PATCH 1/1] credential: do not mask the username

From: Jeff King <peff@peff.net>
Date: Apr 29, 2019, 23:40 UTC
Message-ID: <20190429234028.GA24069@sigill.intra.peff.net>
In-Reply-To: <e459e487d3848ae1b7f37676bd9d2a2f9c967430.1556575570.git.gitgitgadget@gmail.com>

On Mon, Apr 29, 2019 at 03:06:11PM -0700, Jarosław Honkis via GitGitGadget wrote:

Show 9 quoted lines

> From: =?UTF-8?q?Jaros=C5=82aw=20Honkis?= <yaras6@gmail.com>
> 
> When a user is asked for credentials there is no need to mask the
> username, so the PROMPT_ASKPASS flag on calling credential_ask_one for
> login is unnecessary.
> 
> The `credential_ask_one()` function internally uses `git_prompt()` which
> in case it is given the flag PROMPT_ASKPASS uses masked input method
> instead of git_terminal_prompt, which does not mask user input.

This description (and the patch) doesn't make sense to me. The PROMPT_ASKPASS flag is just about whether we would trigger the askpass tool (e.g., if the user does not have a terminal).

The PROMPT_ECHO flag is what you want to tell the underlying code that the value can be shown to the user. And that's already set.

Now there is a slight issue, which is that the askpass tool has no way for us to tell it to show the contents to the user. There's no way around that without disabling askpass entirely, which I guess is the strategy this patch is trying to do. But in doing so it's going to break anybody who _doesn't_ have a terminal, because now we have no way to prompt there for their username!

So I think our options are:

  1. Leave it. If people don't want askpass to prompt them, they should
     not set up askpass.

  2. Use another tool besides askpass. I don't know of any askpass
     implementations that take something like our ECHO flag, but there
     are lots of other tools. I doubt there's any easy portable
     solution, though. And anyway, credential helpers are a much more
     advanced version of this anyway, so I'd probably steer people in
     that direction.

  3. If we really want to try to try to avoid using askpass for
     usernames we can, but I don't think the logic in this patch is
     right.

     If we want to avoid regressing existing cases, then we'd have to
     first check if there's a usable terminal. And only if _that_ fails,
     try askpass. And then give up if neither work. I.e., invert the
     order in git_prompt() when both ASKPASS and ECHO are set.

     I think I'd still favor option 1 over this, though. Configuring
     askpass has always overridden the terminal for usernames, and this
     would change that. I come back to: if you don't want to use
     askpass, then why are you configuring it?

Show 5 quoted lines

>  		c->username = credential_ask_one("Username", c,
> -						 PROMPT_ASKPASS|PROMPT_ECHO);
> +						 (getenv("GIT_ASKPASS") ?
> +						  PROMPT_ASKPASS : 0) |
> +						 PROMPT_ECHO);

This logic is weird. It still uses askpass if GIT_ASKPASS isn't set. But _doesn't_ if it's set elsewhere, e.g. in core.askPass. Which makes little sense to me.

Maybe the intent was that the original user has SSH_ASKPASS set, and that is kicking in (which would also explain why "if you don't like it, don't configure it" didn't work). You can get around that by setting GIT_ASKPASS (or core.askPass) to the empty string (I don't think that's documented anywhere, and I don't recall it being intentional, but it does look like that's how the code works).

-Peff