Request: option to not modify X-Forwarded-For header

[delfer]

Hello!

@fatedier Thank you very much for this beautiful software!!!
I'm using a reverse proxy (https://github.com/containous/traefik) in the front of FRPS and header X-Forwarded-For is already set.
But FRPS always adds a new entry into the list at https://github.com/fatedier/frp/blob/master/utils/vhost/reverseproxy.go#L248
And I have this:

X-Forwarded-For: 3.95.2.106, 127.0.0.1

But my endpoint server (https://github.com/home-assistant/core) does not recognize the list in this header.

Please, add an option to leave X-Forwarded-For header as-is. Thank you!

[fatedier]

I'm confused why https://github.com/home-assistant/core can't support this format?

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Forwarded-For

X-Forwarded-For: <client>, <proxy1>, <proxy2>

ReverseProxy codes are copied from go standard library. I prefer not to modify it.

Maybe you can create an issue of https://github.com/home-assistant/core to solve this problem.

[CzBiX]

home-assistant/core#29868