FR: Support SSH interactive login

[bsdinis]

Is your feature request related to a problem? Please describe.
When doing authentication with Github or having password protected keys, jj does not support receiving these inputs from the user.
Namely, with git.subprocess = true, git is called without stdin open.

Describe the solution you'd like
Have a way to pipe the authentication information back to the user.

Describe alternatives you've considered
The alternatives right now it to not do interactive login. For people that have password protected keys, this is a no-go

[yuja]

Is that platform-dependent issue? On Linux, ssh can obtain tty even if stdin is redirected.

[bsdinis]

Yes, my understanding is that this is a Windows issue that affects both subprocessing and git2

[yuja]

Hmm, then I have no idea how we can fix the problem cleanly. Suppose stdin and stdout of the underlying ssh process are piped, the ssh process might detect tty (or equivalent) through stderr on Windows. However, we need to pipe stderr of the parent git process in order to parse the error message.

If tty is inaccessible, ssh would use ssh-askpass program to open GUI prompt, which wouldn't be available on Windows?

[bsdinis]

The thing here that's confusing to me is the fact that git2 is also not working...

[emilazy]

Perhaps a bisect is in order? (But it might just point to c393555, I suppose.)

[yuja]

The thing here that's confusing to me is the fact that git2 is also not working...

Oh, you mean it was working before but isn't now? iirc, git2 doesn't support interactive SSH prompt.

[bsdinis]

Perhaps a bisect is in order? (But it might just point to c393555, I suppose.)

My main problem is that I can't repro locally, it was reported on discord.
Tbf, I don't think the subprocessing code is at blame. I suspect it was one of the refactorings after.
I'm going to work on trying to find a way to repro

[bsdinis]

Also, I'm not even sure that the issue is an interactive login anymore. Going to try to figure it out