from starlette.datastructures import Headers
from starlette.requests import Request
from starlette.responses import JSONResponse
from starlette.status import HTTP_401_UNAUTHORIZED
from starlette.types import ASGIApp, Receive, Scope, Send

class CasbinMiddleware:
    def __init__(self, app: ASGIApp, enforcer) -> None:
        self.app = app
        self.enforcer = enforcer

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:

        # ToDo Adjust me
        headers = Headers(scope=scope)
        token = headers.get('authorization', None)
        # validate user and get user from token
        user = 'test123'
        #######################################

        request = Request(scope, receive)

        if self.check_permission(user=user, request=request):
            await self.app(scope, receive, send)
            return

        # Invalid request
        response = JSONResponse(
            status_code=HTTP_401_UNAUTHORIZED,
            content="Insufficient permissions",
            headers={"WWW-Authenticate": "Bearer"},
        )

        await response(scope, receive, send)
        return

    def check_permission(self, user: str, request: Request):
        path = request.path
        method = request.method
        return self.enforcer.enforce(user, path, method)

from middleware import CasbinMiddleware
import casbin
...
enforcer = casbin.Enforcer("authz_model.conf", "authz_policy.csv")
app.add_middleware(CasbinMiddleware,enforcer=enforcer)