Hi,
I'm trying to build a FastAPI app with a reverse proxy. It sends the requests to a remote server, then modifies the response. It mostly works. However when it sits behind Cloudfront and makes a request to another Cloudfront endpoint (CF1 -> FastAPI -> CF2), I get 403 errors. It seems that it is linked to having a "via" header.
I'm trying to remove that header before sending the request, but when I do that, I get an Exception in ASGI application.

Here is the relevant part of the code:

proxy = ReverseHttpProxy(AsyncClient(), base_url=f"http://{fqdn}/")
@app.api_route("/{path:path}", methods=["GET", "HEAD", "OPTIONS"])
async def _(request: Request, path: str = ""):
 
 # Remove the "via" header. 
 if "Via" in request.headers:
 request.headers = MutableHeaders(dict(request.headers.items()))
 del request.headers["Via"]
 proxy_response = await proxy.proxy(request=request, path=path)
 query_params = dict(request.query_params)
 return proxy_response

If I comment the if statement, no issue (other than the 403 obviously).

Any idea what I'm doing wrong?