Re: git credential cache timeout questions

Thanks. Now that I know it is a rolling timeout, I was able to narrow
my search for anything that might be causing the timer to extend.

There is a git helper program I use that has a background refresh that
I think I must leave open overnight sometimes. I think this was
causing my timeout to be extended. I disabled the background refresh
task and the timeout seems to be expiring like I expect now.

--John

On Fri, Feb 19, 2021 at 12:04 PM Jeff King [off-list ref] wrote:

On Fri, Feb 19, 2021 at 10:46:48AM -0500, John Ratliff wrote:

quoted

I have configured my git to cache my credentials for 12 hours using
this section in my .gitconfig

[credential "https://mygithub.example.edu"]
    username = myuser
    helper = cache --timeout 43200

However, the credentials don’t always seem to expire after 12 hours.
Sometimes I come back the next morning and the credentials still work.
This is generally after leaving at 5:00 PM and coming back in the next
day at 9:00 AM, well past the 12 hour timeout.

Is there any way to see the current timeout value? Is it a rolling
timeout (i.e. any git action resets the timeout)?

It's the "rolling" thing, though the source is a bit subtle. The
credential-cache helper sets an absolute expiration when the value is
stored, and it doesn't update it on a "get" request.

However, Git's interaction with the helpers is generally:

  - when we need a credential ask for one

  - when a credential is rejected by a server, tell helpers to erase it

  - when a credential is accepted by a server, tell helpers to store it

And it's that last one that provides the rolling timeout, because we do
it even if the credential came from a helper in the first place!

I actually wrote a patch long ago to switch this behavior:

  https://lore.kernel.org/git/20120407033417.GA13914@sigill.intra.peff.net/ (local)

But it turned out some people actually rely on it. :)

There's some discussion in that thread about paths forward, and I think
I even played around with it back then. But then it sat on my todo list,
and now it has been 9 years, so I don't remember if there were good
reasons not to push it forward, or if I simply never got around to it (I
suspect the latter; nobody had a pressing use case that was solved by
avoiding the rolling timeouts, it just seemed to me to be a bit less
surprising). I'd be happy if somebody wanted to revisit the topic.

(To your other question, "is there a way to see the timeout value", the
answer is "not really, without running it under gdb". I wouldn't be
opposed to adding more diagnostic output to the daemon. But you can also
see some of what's going on by setting GIT_TRACE=1 in the environment,
which will show the extra "store" operation being done by Git).

-Peff