On Mon, Oct 24, 2022 at 07:59:22PM -0400, Jeff King wrote:

We did discuss patches a long time ago that would let Git carry
arbitrary keys between helpers, even if Git itself didn't understand it.
One of the intended uses was to let helpers talk to each other about
TTLs. So if you had say:

  [credential]
  helper = generate-some-token
  helper = cache

where the first helper generates a token, and the second caches it, the
first one could shove a "ttl" or "expiration" key into the protocol,
which the cache could then learn to respect.

In case anyone is morbidly curious, it was in this thread:

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

-Peff