This is a new form of authentication for Google services, where instead
of passing a signed claim to obtain a token from the OAuth endpoint, you
present the signed claim *as* the token to the API endpoint.
Fixes#139.
Fixes#140.
Change-Id: Ibf0f168a0ec111660ac08b86121c943fb96e146c
Reviewed-on: https://go-review.googlesource.com/10667
Reviewed-by: David Symonds <dsymonds@golang.org>
Reviewed-by: Dave Day <djd@golang.org>
Andrew Gerrand