How to integrate casbin watcher in fastapi

[YihuiLu]

Example

Here's a self-contained, minimal, reproducible, example with my use case:

import uvicorn
from app import create_app

app = create_app()

if __name__ == "__main__":
    uvicorn.run("main:app", host="0.0.0.0", port=7780, reload=True)


# app

def create_app():
    app = FastAPI(
        title=settings.PROJECT_NAME, openapi_url=f"{settings.API_V1_STR}/openapi.json"
    )

    # Set all CORS enabled origins
    if settings.BACKEND_CORS_ORIGINS:
        app.add_middleware(
            CORSMiddleware,
            allow_origins=[str(origin) for origin in settings.BACKEND_CORS_ORIGINS],
            allow_credentials=True,
            allow_methods=["*"],
            allow_headers=["*"],
        )

    app.include_router(api_router, prefix=settings.API_V1_STR)

    # add_authentication_middleware(app)

    register_redis(app)
    register_casbin(app)

    return app


def add_authentication_middleware(app: FastAPI):
    class BasicAuth(AuthenticationBackend):
        async def authenticate(self, request):
            if "Authorization" not in request.headers:
                return None

            auth = request.headers["Authorization"]
            try:
                scheme, credentials = auth.split()
                decoded = base64.b64decode(credentials).decode("ascii")
            except (ValueError, UnicodeDecodeError, binascii.Error):
                raise AuthenticationError("Invalid basic auth credentials")

            username, _, password = decoded.partition(":")
            return AuthCredentials(["authenticated"]), SimpleUser(username)

    model_file_path = Path(__file__).parent / "core/configs/casbin_model.conf"
    model_file_path = str(model_file_path.absolute())

    adapter = casbin_sqlalchemy_adapter.Adapter(settings.SQLALCHEMY_DATABASE_URI)

    enforcer = casbin.Enforcer(model_file_path, adapter, settings.CASBIN_LOG)

    watcher = RedisWatcher(
        settings.CASBIN_REDIS_WATCHER_HOST, settings.CASBIN_REDIS_WATCHER_PORT
    )
    watcher.set_update_callback(enforcer.load_policy)
    enforcer.set_watcher(watcher)

    app.add_middleware(CasbinMiddleware, enforcer=enforcer)
    app.add_middleware(AuthenticationMiddleware, backend=BasicAuth())


def register_redis(app: FastAPI) -> None:
    @app.on_event("startup")
    async def create_redis():
        app.state.redis = await RedisPool()

    @app.on_event("shutdown")
    async def close_redis():
        app.state.redis.close_pool()


def register_casbin(app: FastAPI) -> None:
    @app.on_event("startup")
    def create_casbin():
        model_file_path = Path(__file__).parent / "core/configs/casbin_model.conf"
        model_file_path = str(model_file_path.absolute())
        adapter = casbin_sqlalchemy_adapter.Adapter(settings.SQLALCHEMY_DATABASE_URI)
        enforcer = casbin.Enforcer(model_file_path, adapter, settings.CASBIN_LOG)
        # watcher = NewRedisWatcher(
        #     settings.CASBIN_REDIS_WATCHER_HOST, settings.CASBIN_REDIS_WATCHER_PORT,
        #     settings.CASBIN_REDIS_WATCHER_PASSWORD, settings.CASBIN_REDIS_WATCHER_DB
        # )
        watcher = RedisWatcher(
            settings.CASBIN_REDIS_WATCHER_HOST, settings.CASBIN_REDIS_WATCHER_PORT
        )
        app.state.enforcer = enforcer
        watcher.set_update_callback(app.state.enforcer.load_policy)
        enforcer.set_watcher(watcher)
        app.state.enforcer = enforcer

Description

I wanted to use FastApi with Casbin, and everything went well until I deployed FastApi and found that Casbin's permission data couldn't be synchronized when the permissions were modified because Ucicoorn started multiple FastApi instances, so I found a way to use Watcher sync permission information in the Casbin community, but because Watcher didn't support FastApi well, there were the following issues:
ScienceLogic/pycasbin-redis-watcher#2

After discussion, it was suggested that I use fastapi-authz, but after trying, the following questions a
pycasbin/fastapi-authz#13

So, I wonder if it's possible to resolve this issue with FastApi?

Environment

• OS: [macOS]:
• FastAPI Version [e.g. 0.63.0]:

[hsluoyz]

@Zxilly @ffyuanda