Google-auth

- ``transports.grpc.secure_authorized_channel`` now passes ``kwargs`` to ``grpc.secure_channel``. ([90](https://github.com/googleapis/google-auth-library-python/pull/90))
- Added new property ``credentials.Singing.signer_email`` which can be used to identify the signer of a message. ([89](https://github.com/googleapis/google-auth-library-python/pull/89))
- (google_auth_httplib2) Added a proxy to ``httplib2.Http.connections``.

- Fixed an issue where an ``ImportError`` would occur if ``google.oauth2`` was imported before ``google.auth``. ([88](https://github.com/googleapis/google-auth-library-python/pull/88))

- Fixed a bug where non-padded base64 encoded strings were not accepted. ([87](https://github.com/googleapis/google-auth-library-python/pull/87))
- Fixed a bug where ID token verification did not correctly call the HTTP request function. ([87](https://github.com/googleapis/google-auth-library-python/pull/87))

- Added Google ID token verification helpers. ([82](https://github.com/googleapis/google-auth-library-python/pull/82))
- Swapped the ``target`` and ``request`` argument order for ``grpc.secure_authorized_channel``. ([81](https://github.com/googleapis/google-auth-library-python/pull/81))
- Added a user's guide. ([79](https://github.com/googleapis/google-auth-library-python/pull/79))
- Made ``service_account_email`` a public property on several credential classes. ([76](https://github.com/googleapis/google-auth-library-python/pull/76))
- Added a ``scope`` argument to ``google.auth.default``. ([75](https://github.com/googleapis/google-auth-library-python/pull/75))
- Added support for the ``GCLOUD_PROJECT`` environment variable. ([73](https://github.com/googleapis/google-auth-library-python/pull/73))

- Added gRPC support. ([67](https://github.com/googleapis/google-auth-library-python/pull/67))
- Added Requests support. ([66](https://github.com/googleapis/google-auth-library-python/pull/66))
- Added ``google.auth.credentials.with_scopes_if_required`` helper. ([65](https://github.com/googleapis/google-auth-library-python/pull/65))
- Added private helper for oauth2client migration. ([70](https://github.com/googleapis/google-auth-library-python/pull/70))

First release with core functionality available. This version is ready for
initial usage and testing.

- Added ``google.auth.credentials``, public interfaces for Credential types. ([8](https://github.com/googleapis/google-auth-library-python/pull/8))
- Added ``google.oauth2.credentials``, credentials that use OAuth 2.0 access and refresh tokens ([24](https://github.com/googleapis/google-auth-library-python/pull/24))
- Added ``google.oauth2.service_account``, credentials that use Service Account private keys to obtain OAuth 2.0 access tokens. ([25](https://github.com/googleapis/google-auth-library-python/pull/25))
- Added ``google.auth.compute_engine``, credentials that use the Compute Engine metadata service to obtain OAuth 2.0 access tokens. ([22](https://github.com/googleapis/google-auth-library-python/pull/22))
- Added ``google.auth.jwt.Credentials``, credentials that use a JWT as a bearer token.
- Added ``google.auth.app_engine``, credentials that use the Google App Engine App Identity service to obtain OAuth 2.0 access tokens. ([46](https://github.com/googleapis/google-auth-library-python/pull/46))
- Added ``google.auth.default()``, an implementation of Google Application Default Credentials that supports automatic Project ID detection. ([32](https://github.com/googleapis/google-auth-library-python/pull/32))
- Added system tests for all credential types. ([51](https://github.com/googleapis/google-auth-library-python/pull/51), [#54](https://github.com/googleapis/google-auth-library-python/pull/54), [#56](https://github.com/googleapis/google-auth-library-python/pull/56), [#58](https://github.com/googleapis/google-auth-library-python/pull/58), [#59](https://github.com/googleapis/google-auth-library-python/pull/59), [#60](https://github.com/googleapis/google-auth-library-python/pull/60), [#61](https://github.com/googleapis/google-auth-library-python/pull/61), [#62](https://github.com/googleapis/google-auth-library-python/pull/62))
- Added ``google.auth.transports.urllib3.AuthorizedHttp``, an HTTP client that includes authentication provided by credentials. ([19](https://github.com/googleapis/google-auth-library-python/pull/19))
- Documentation style and formatting updates.