Release v1.23.0

• Make API-specific endpoints default for batch requests
• Make multipart/mixed requests in compiliance with RFC7230

Release v1.21.0

• Make constructors of GoogleJsonResponseException, GoogleAuthIOException, GooglePlayServicesAvailabilityIOException, and UserRecoverableAuthIOException public to allow creating tests that throw them
• Fix for missing newline when GET requests are embedded in multipart requests
• Add support for retrieving credentials in the Cloud Shell environment. Due to server-side changes between the feature addition and the release, this feature is broken in this release but is already fixed for the next release.
• Add https://accounts.google.com as a valid issuer id in GoogleIdTokenVerifier. The previous id accounts.google.com still validates