[Python] Can't access path parameters from middleware

My typical path is something like

/user/{user_id}/resource/{resource_id}


I have a validation method, already written in async Python, like this:

async def is_allowed(user_id: int, resource_id: int) -> bool


That returns a boolean: True if the user can access the resource, False otherwise.

I want to write a middleware that calls is_allowed extracting the variables from the path.

I fiddled around but I can't find how to get them: I was expecting to get this information from request.path_params.

A more complete example:

import logging

from fastapi import FastAPI
from starlette.requests import Request
from starlette.responses import Response

app = FastAPI()

_logger = logging.getLogger()
_logger.setLevel(logging.DEBUG)


async def is_allowed(user_id, resource_id):
_logger.error(user_id)
_logger.error(resource_id)
return True


@app.middleware('http')
async def acl(request: Request, call_next):
user_id = request.path_params.get("user_id", None)
resource_id = request.path_params.get("resource_id", None)
allowed = await is_allowed(user_id, resource_id)
if not allowed:
return Response(status_code=403)
else:
return await call_next(request)


@app.get('/user/{user_id}/resource/{resource_id}')
async def my_handler(user_id: int, resource_id: int):
return {"what": f"Doing stuff with {user_id} on {resource_id}"}


The logged values are None.

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