Introduce new AuthenticationError type returned by
errWrappingTokenSource.Token. The new error wrapper
exposes a boolean method Temporary, identifying the
underlying network error as retryable based on the
following status codes: 500, 503, 408, or 429.
Bump go.mod version to 1.15
refs: https://github.com/googleapis/google-api-go-client/issues/1445
Change-Id: I27c76cb0c71b918c25a640f40d0bd515b2e488fc
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/403846
Reviewed-by: Cody Oss <codyoss@google.com>
Reviewed-by: Tyler Bui-Palsulich <tbp@google.com>
Chris Smith