Add support for proxypass middleware

[signebedi]

Werkzeug allowed us to do this in one line of code, but I'm not sure if starlette can do the same...

[signebedi]

Based on https://pypi.org/project/fastapi-proxiedheadersmiddleware/, we might be able to use the following code:

from typing import List, Tuple

from starlette.types import ASGIApp, Receive, Scope, Send

Headers = List[Tuple[bytes, bytes]]


class ProxiedHeadersMiddleware:
    """
    A middleware that modifies the request to ensure that FastAPI uses the
    X-Forwarded-* headers when creating URLs used to reference this application.

    We are very permissive in allowing all X-Forwarded-* headers to be used, as
    we know that this API will be published behind the API Gateway, and is
    therefore not prone to redirect hijacking.

    """

    def __init__(self, app: ASGIApp):
        self.app = app

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        scope["headers"] = self.remap_headers(scope.get("headers", {}))

        await self.app(scope, receive, send)
        return

    def remap_headers(self, source: Headers) -> Headers:
        """
        Map X-Forwarded-Host to host and X-Forwarded-Prefix to prefix.

        """

        source = dict(source)

        if b'x-forwarded-host' in source:
            source.update({b'host': source[b'x-forwarded-host']})
            source.pop(b'x-forwarded-host')

        if b'x-forwarded-prefix' in source:
            source.update({
                b'host': source[b'host'] + source[b'x-forwarded-prefix']
            })
            source.pop(b'x-forwarded-prefix')

        source = [(k, v) for k, v in source.items()]

        return source

Source https://gitlab.developers.cam.ac.uk/uis/devops/lib/fastapi-proxiedheadersmiddleware/-/blob/main/fastapi_proxiedheadersmiddleware/__init__.py?ref_type=heads