Removing a header before proxying the request

[wabiloo]

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?

[WSH032]

Hi @wabiloo

I get an Exception in ASGI application

Can you send me the complete exception traceback?

[wabiloo]

Hi, not sure how to get that. I couldn't figure it out.

I'll try and give you a piece of code that you can run and that reproduces it

[WSH032]

Hi, not sure how to get that. I couldn't figure it out.

just send me the terminal output, it might look something like this:

PS E:\GitHub\fastapi-proxy> python  
Python 3.10.8 (tags/v3.10.8:aaaf517, Oct 11 2022, 16:50:30) [MSC v.1933 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> a
Traceback (most recent call last):   
    File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined  

I'll try and give you a piece of code that you can run and that reproduces it

it's best to be a minimal reproducible example