plg Send Custom Header
This is the plugin referred to in Making your Joomla Site fly with NGinx reverse proxy caching.
It was originally written for Joomla 2.5/3.x and there hasn't been any development on it in several years - it's no longer supported in any way.
I've not tested against Joomla 4, so it may or may not work.
Copyright (c) 2013 B Tasker
Released under GNU GPL V2, see LICENSE