How do I add the origin IP to a response header?

I’m looking for options to add a new response header with the origin IP that replied to a request. I’ve looked at the available fields at Available fields and functions for HTTP response header modification · Cloudflare Rules docs for http_response_headers_transform phase but not seeing anything similar.

Origin IP, as in the IP of the web server/your server which Cloudflare sent the request to? As far as I know, simply not a field for it, not one documented or guessable at least. The response fields are pretty limited. You can get the client’s IP, and the IP of the CF IP they connected to. You could potentially have your origin itself respond with it’s IP in a header.