Bassam Ojeil f145937023 google: update documentation for workload identity federation
Document using workload identity federation from non-Google Cloud platforms to access Google Cloud resources.
This covers federation from AWS, Azure and OIDC providers via Application Default Credentials.

Change-Id: I77ee7f6aac5a75d095304f07f3004ec3fb7b9613
GitHub-Last-Rev: 07c9dd02716519190b63275be2fb3cf1c4bb6b1d
GitHub-Pull-Request: golang/oauth2#478
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/293751
Reviewed-by: Cody Oss <codyoss@google.com>
Trust: Cody Oss <codyoss@google.com>
Trust: Tyler Bui-Palsulich <tbp@google.com>
Run-TryBot: Cody Oss <codyoss@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
2021-02-18 20:13:42 +00:00
..
2016-07-19 16:36:24 +00:00