Added authhandler.go, which implements a TokenSource to support "three-legged OAuth 2.0" via a custom AuthorizationHandler.
Added example_test.go with a sample command line implementation for AuthorizationHandler.
This patch adds support for 3-legged-OAuth flow using an OAuth Client ID file downloaded from Google Cloud Console.
Change-Id: Iefe54494d6f3ee326a6b1b2a81a7d5d1a7ba3331
GitHub-Last-Rev: 48fc0367c2
GitHub-Pull-Request: golang/oauth2#419
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/232238
Reviewed-by: Tyler Bui-Palsulich <tbp@google.com>
Reviewed-by: Shin Fan <shinfan@google.com>
Reviewed-by: Cody Oss <codyoss@google.com>
Trust: Shin Fan <shinfan@google.com>
Trust: Cody Oss <codyoss@google.com>
Andy Zhao