Log Message:
Updated py-oauth2client to 4.0.0.

## v4.0.0

New features:
* New Django samples. (#636)
* Add support for RFC7636 PKCE. (#588)
* Release as a universal wheel. (#665)

Bug fixes:
* Fix django authorization redirect by correctly checking validity of \ 
credentials. (#651)
* Correct query loss when using parse_qsl to dict. (#622)
* Switch django models from pickle to jsonpickle. (#614)
* Support new MIDDLEWARE Django 1.10 aetting. (#623)
* Remove usage of os.environ.setdefault. (#621)
* Handle missing storage files correctly. (#576)
* Try to revoke token with POST when getting a 405. (#662)

Internal changes:
* Use transport module for GCE environment check. (#612)
* Remove __author__ lines and add contributors.md. (#627)
* Clean up imports. (#625)
* Use transport.request in tests. (#607)
* Drop unittest2 dependency (#610)
* Remove backslash line continuations. (#608)
* Use transport helpers in system tests. (#606)
* Clean up usage of HTTP mocks in tests. (#605)
* Remove all uses of MagicMock. (#598)
* Migrate test runner to pytest. (#569)
* Merge util.py and _helpers.py. (#579)
* Remove httplib2 imports from non-transport modules. (#577)

Breaking changes:
* Drop Python 3.3 support. (#603)
* Drop Python 2.6 support. (#590)
* Remove multistore_file. (#589)

## v3.0.0

* Populate `token_expiry` for GCE credentials. (#473)
* Move GCE metadata interface to a separate module. (#520)
* Populate `scopes` for GCE credentials. (#524)
* Fix Python 3.5 compatibility. (#531)
* Add `oauth2client.contrib.sqlalchemy`, a SQLAlchemy-based credential store. (#527)
* Improve error when an invalid client secret is provided. (#530)
* Add `oauth2client.contrib.multiprocess_storage`. This supersedes the \ 
functionality in `oauth2client.contrib.multistore_file`. (#504)
* Pull httplib2 usage into a separate transport module. (#559, #561)
* Refactor all django-related code into `oauth2client.contrib.django_util`. Add \ 
`DjangoORMStorage`, remove `FlowField`. (#546)
* Fix application default credentials resolution order. (#570)
* Add configurable timeout for GCE metadata server check. (#571)
* Add warnings when using deprecated `approval_prompt='force'`. (#572)
* Add deprecation warning to `oauth2client.contrib.multistore_file`. (#574)
* (Hygiene) PEP8 compliance and various style fixes (#537, #540, #552, #562)
* (Hygiene) Remove duplicated exception classes in \ 
`oauth2client.contrib.appengine`. (#533)

NOTE: The next major release of oauth2client (v4.0.0) will remove the \ 
`oauth2client.contrib.multistore_file` module.

## v2.2.0

* Added support to override `token_uri` and `revoke_uri` in \ 
`oauth2client.service_account.ServiceAccountCredentials`. (#510)
* `oauth2client.contrib.multistore_file` now handles `OSError` in addition to \ 
`IOError` because Windows may raise `OSError` where other platforms will raise \ 
`IOError`.
* `oauth2client.contrib.django_util` and `oauth2client.contrib.django_orm` have \ 
been updated to support Django 1.8 - 1.10. Versions of Django below 1.8 will not \ 
work with these modules.

## v2.1.0

* Add basic support for JWT access credentials. (#503)
* Fix `oauth2client.client.DeviceFlowInfo` to use UTC instead of the system \ 
timezone when calculating code expiration.

## v2.0.2

* Fix issue where `flask_util.UserOAuth2.required` would accept expired \ 
credentials (#452).
* Fix issue where `flask_util` would fill the session with `Flow` objects (#498).
* Fix issue with Python 3 binary strings in `Flow.step2_exchange` (#446).
* Improve test coverage to 100%.

## v2.0.1

* Making scopes optional on Google Compute Engine `AppAssertionCredentials`
  and adding a warning that GCE won't honor scopes (#419)
* Adding common `sign_blob()` to service account types and a
  `service_account_email` property. (#421)
* Improving error message in P12 factory
  `ServiceAccountCredentials.from_p12_keyfile` when pyOpenSSL is
  missing. (#424)
* Allowing default flags in `oauth2client.tools.run_flow()`
  rather than forcing users to create a dummy argparser (#426)
* Removing `oauth2client.util.dict_to_tuple_key()` from public
  interface (#429)
* Adding `oauth2client.contrib._appengine_ndb` helper module
  for `oauth2client.contrib.appengine` and moving most code that
  uses the `ndb` library into the helper (#434)
* Fix error in `django_util` sample code (#438)

## v2.0.0-post1

* Fix Google Compute Engine breakage (#411, breakage introduced in #387) that
  made it impossible to obtain access tokens
* Implement `ServiceAccountCredentials.from_p12_keyfile_buffer()`
  to allow passing a file-like object in addition to the factory
  constructor that uses a filename directly (#413)
* Implement `ServiceAccountCredentials.create_delegated()`
  to allow upgrading a credential to one that acts on behalf
  of a given subject (#420)