Revamp authentication (#831)

* Implement Transport classes

* Implement authentication strategy classes

* Revamp authentication with Transport and Strategy

* Revamp strategy and OAuth so that they can use a callable dependency

* Update docstring

* Make ErrorCode a proper Enum and cleanup unused OpenAPI utils

* Remove useless check

* Tweak typing in authenticator

* Update docs

* Improve logout/destroy token logic

* Update docs

* Update docs

* Update docs and full examples

* Apply formatting to examples

* Update OAuth doc and examples

* Add migration doc

* Implement Redis session token

* Add Redis Session documentation

* RedisSession -> Redis

* Fix links in docs

tests/test_authentication_backend.py

@@ -0,0 +1,60 @@
+from typing import Callable, Generic, Optional, Type
+
+import pytest
+from fastapi import Response
+
+from fastapi_users import models
+from fastapi_users.authentication import (
+    AuthenticationBackend,
+    BearerTransport,
+    Strategy,
+)
+from fastapi_users.authentication.strategy import StrategyDestroyNotSupportedError
+from fastapi_users.authentication.transport.base import Transport
+from fastapi_users.manager import BaseUserManager
+from tests.conftest import MockStrategy, MockTransport, UserDB
+
+
+class MockTransportLogoutNotSupported(BearerTransport):
+    pass
+
+
+class MockStrategyDestroyNotSupported(Strategy, Generic[models.UC, models.UD]):
+    async def read_token(
+        self, token: Optional[str], user_manager: BaseUserManager[models.UC, models.UD]
+    ) -> Optional[models.UD]:
+        return None
+
+    async def write_token(self, user: models.UD) -> str:
+        return "TOKEN"
+
+    async def destroy_token(self, token: str, user: models.UD) -> None:
+        raise StrategyDestroyNotSupportedError
+
+
+@pytest.fixture(params=[MockTransport, MockTransportLogoutNotSupported])
+def transport(request) -> Transport:
+    transport_class: Type[BearerTransport] = request.param
+    return transport_class(tokenUrl="/login")
+
+
+@pytest.fixture(params=[MockStrategy, MockStrategyDestroyNotSupported])
+def get_strategy(request) -> Callable[..., Strategy]:
+    strategy_class: Type[Strategy] = request.param
+    return lambda: strategy_class()
+
+
+@pytest.fixture
+def backend(
+    transport: Transport, get_strategy: Callable[..., Strategy]
+) -> AuthenticationBackend:
+    return AuthenticationBackend(
+        name="mock", transport=transport, get_strategy=get_strategy
+    )
+
+
+@pytest.mark.asyncio
+@pytest.mark.authentication
+async def test_logout(backend: AuthenticationBackend, user: UserDB):
+    result = await backend.logout(backend.get_strategy(), user, "TOKEN", Response())
+    assert result is None