Update authlib to 0.8

[pyup-bot]

This PR updates authlib from 0.7 to 0.8.

Changelog

0.8

- RFC7523: Add JWTs for Client Authentication of :ref:`specs/rfc7523`.
- OIDC: Add ``response_mode=form_post`` support for OpenID Connect.

**Improvement** in this release:

- A new redesigned error system. All errors are subclasses of a ``AuthlibBaseError``.
- I18N support for error descriptions.
- Separate AuthorizationCodeMixin in ``authlib.flask.oauth2.sqla`` via :gh:`issue57`.
- Add context information when generate token via :gh:`issue58`.
- Improve JWT key handles, auto load JWK and JWK set.
- Add ``require_oauth.acquire`` with statement, get example on :ref:`flask_oauth2_server`.

**Deprecate Changes**: find how to solve the deprecate issues via https://git.io/vhL75

- Rename config key ``OAUTH2_EXPIRES_IN`` to ``OAUTH2_TOKEN_EXPIRES_IN``.
- Rename Flask OAuth 2.0 ``create_expires_generator`` to
``create_token_expires_in_generator``

Links

• PyPI: https://pypi.org/project/authlib
• Changelog: https://pyup.io/changelogs/authlib/
• Homepage: https://authlib.org/