CORSMiddleware with optional callback

[Jontpan]

We have a use case where an optional callback to the CORSMiddleware is hugely useful. Would a PR for something like this be (eventually) accepted?

class CORSMiddleware:
    def __init__(
        self,
        app: ASGIApp,
        allow_origins: typing.Sequence[str] = (),
        allow_methods: typing.Sequence[str] = ("GET",),
        allow_headers: typing.Sequence[str] = (),
        allow_credentials: bool = False,
        allow_origin_regex: str | None = None,
        expose_headers: typing.Sequence[str] = (),
        max_age: int = 600,
        callback: typing.Optional[typing.Callable[[str], bool]] = None,
    ) -> None:
        ...
        self.callback = callback

    ...

    async def is_allowed_origin(self, origin: str) -> bool:
        if self.allow_all_origins:
            return True

        if self.allow_origin_regex is not None and self.allow_origin_regex.fullmatch(
            origin
        ):
            return True

        # Check static origins first
        if origin in self.allow_origins:
            return True

        if self.callback is not None:
            return await self.callback(origin)

        return False

[Kludex]

You can subclass CORSMiddleware, and overwrite the is_allowed_origin method.

[Jontpan]

Fair enough. Any chance of making is_allowed_origin async?

[Kludex]

You can create your own CORSMiddleware if you need that.