curl/docs/cmdline-opts/haproxy-protocol.md

c	SPDX-License-Identifier	Long	Help	Protocols	Added	Category	Multi	See-also	Example
Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.	curl	haproxy-protocol	Send HAProxy PROXY protocol v1 header	HTTP	7.60.0	http proxy	boolean	proxy	--haproxy-protocol $URL

--haproxy-protocol

Send a HAProxy PROXY protocol v1 header at the beginning of the connection. This is used by some load balancers and reverse proxies to indicate the client's true IP address and port.

This option is primarily useful when sending test requests to a service that expects this header.