Token caching is now done whenever you make a Client, and
ReuseTokenSource is exported from the oauth2 package and used by the
Google TokenSources (Compute and App Engine).
Token.Expired is now Token.Valid, and works on nil receivers.
Some other wording cleanups in the process.
All tests pass. App Engine should pass, but is untested.
Change-Id: Ibe1d2599ac3ccfe9b399b1672f74bb24cfc8d311
Reviewed-on: https://go-review.googlesource.com/2195
Reviewed-by: Burcu Dogan <jbd@google.com>
- Reduce the duplicate code by merging the flows and
determining the flow type by looking at the provided options.
- Options as a function type allows us to validate an individual
an option in its scope and makes it easier to compose the
built-in options with the third-party ones.