Improvements on authentication documentation (#1420)
Improvements on authentication documentation (#1420)

* Use `conn` in `AuthenticationBackend` documentation

* Remove unused import in `AuthenticationBackend` documentation

* Add missing imports in authentication documentation

Co-authored-by: Marcelo Trylesinski <5c86bce04fb7a3515a6d5a7f8f4be0d0fd9bf2f8@gmail.com>
encode/starlette,encode/starlette