Google is moving toward a default, language-agnostic way of obtaining
authentication credentials on App Engine and Compute Engine.
This change implements this mechanism.
Fixes#90.
Change-Id: Iaae4d60bbc75b1a9f2ec6ad14ab76fb2e279d756
Reviewed-on: https://go-review.googlesource.com/6074
Reviewed-by: Burcu Dogan <jbd@google.com>
Andrew Gerrand