Add support for "expires_in" field in authentication response

Per the documentation [1], the "expires_in" field is preferred over
the "expires_at" field.

Refactor the implementation to hold the instant at which the token was
issued, along with the expiry period, and calculate the "expires_at"
value on demand.

[1] https://github.com/git-lfs/git-lfs/blob/master/docs/api/authentication.md

Change-Id: I14a05e5d71254ecacf36655a341d60febed8531e
9 files changed
tree: de9477ce3f311748c7ece5b6fab3e41eedd17743
  1. src/
  2. tools/
  3. .gitignore
  4. bazlets.bzl
  5. BUILD
  6. external_plugin_deps.bzl
  7. WORKSPACE