Summary

Adding requires('scope') to a function that has a request param that is not of type Request currently throws an AssertionError:

  File ".venv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 1002, in run
    result = context.run(func, *args)
  File ".venv/lib/python3.14/site-packages/starlette/authentication.py", line 79, in sync_wrapper
    assert isinstance(request, Request)
           ~~~~~~~~~~^^^^^^^^^^^^^^^^^^
AssertionError

Which isn't much of a problem specifically in starlette since all functions that handle post requests will do so from accessing request.json(). However, in fastapi, body parameters are pydantic models that can be any name and type, including request.

This change is to add a message to the assert to better communicate what the issue might be for the case where the request parameter is not of type Request:

  File ".venv/lib/python3.14/site-packages/anyio/_backends/_asyncio.py", line 1002, in run
    result = context.run(func, *args)
  File ".venv/lib/python3.14/site-packages/starlette/authentication.py", line 84, in sync_wrapper
    assert isinstance(request, Request), (
           ~~~~~~~~~~^^^^^^^^^^^^^^^^^^
AssertionError: Parameter with name 'request' is required to be of type 'Request' not 'ExampleRequest'

MRE:

import fastapi
import uvicorn
from starlette.authentication import AuthenticationBackend, AuthCredentials, SimpleUser, requires
from starlette.middleware import Middleware
from starlette.middleware.authentication import AuthenticationMiddleware
from starlette.responses import PlainTextResponse
import pydantic


class ExampleRequest(pydantic.BaseModel):
    name: str


class BasicAuthBackend(AuthenticationBackend):
    async def authenticate(self, conn):
        return AuthCredentials(["authenticated"]), SimpleUser("username")


middleware = [
    Middleware(AuthenticationMiddleware, backend=BasicAuthBackend())
]

app = fastapi.FastAPI(middleware=middleware)



@app.post("/")
@requires("authenticated")
def example(request: ExampleRequest):
    return PlainTextResponse(f'Hello, {request.name}!')


uvicorn.run(app, host='0.0.0.0', port=8000)

curl -X 'POST' \
  'http://127.0.0.1:8000/' \
  -H 'accept: application/json' \
  -H 'Content-Type: application/json' \
  -d '{
  "name": "string"
}'

Changing request: ExampleRequest to body: ExampleRequest and adding a request: Request to the function params above works fine.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change. non functional change
• I've updated the documentation accordingly.