git credential cache timeout questions

git credential cache timeout questions

[John Ratliff]

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)?

If it happened once or twice, I would assume I just forgot that I did
something with git later than I thought. But this happens frequently
enough that it’s difficult to accept that as a possibility. It’s not a
daily occurrence. My credentials do expire…I just have no idea when
they will.

Have I setup my gitconfig section wrong?

CentOS 7. Git 2.24.3.

Thanks.


--John

Re: git credential cache timeout questions

[Jeff King]

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

> 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/

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

Re: git credential cache timeout questions

[John Ratliff]

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 <peff@peff.net> wrote:
>
> On Fri, Feb 19, 2021 at 10:46:48AM -0500, John Ratliff wrote:
>
> > 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/
>
> 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