FastAPI middleware to substitute X-Forwarded-Uri and X-Forwarded-Host

Question

I'm new with FastAPI and Starlette, and I'm struggling to make a middleware that tampers the incoming request. I'm trying to parse the X-Forwarded-Uri and the X-Forwarded-Host headers and modify the incoming request so that those are taken into account instead of the actual request.

My attempt is the following piece of code:

class XForwardedMiddleware(BaseHTTPMiddleware):
    async def dispatch(self, request, call_next):
        for header, value in request.scope["headers"]:
            if header == b"x-forwarded-uri":
                uri = URL(value.decode("utf-8"))
                request.scope["path"] = uri.path
                request.scope["query_string"] = uri.query.encode("utf-8")
            if header == b"x-forwarded-host":
                request.scope["headers"].append((b"host", value))

        response = await call_next(request)
        return response

However, it fails to identify the base_url of the request and fails when I use request.url_for('/some/route') as it returns the location of the actual request instead of the 'X-Fowarded' one.