Where are the variables usable when adding extra headers?

[WoJ]

I would like to add an extra header in my proxy call to the upstream server (Caddy V2). To do that I can use header_up

reverse_proxy localhost:9000 {
	header_up Hello-World "Bonjour everyone!"
}

(I will be using the API to configure the routes, so this will be the JSON version, appropriate for the API)

I need however to add a header X-Real-IP which has the value of the calling client - the value which is added to X-Forwarded-For.

Where is this value stored? And generally speaking - is there a list of all the variables which are usable when the call goes though the various layers?

[WoJ]

OK - I think I found the place: Caddyfile Concepts — Caddy Documentation

In my case this is {http.request.remote} {http.request.remote.host} (otherwise I get host+port).

Note for future readers (including myself): the word to search for is “placeholders”.

[francislavoie]

Unfortunately the list of placeholders is a bit scattered because each module provides their own. For the HTTP app, the complete list is here:

JSON Config Structure - Caddy Documentation

The page you linked is the list of placeholders that the Caddyfile provides shortcuts for, not necessarily the full list of placeholders available.

In your case, you can use {remote_host} instead of {http.request.remote.host} because of the Caddyfile shortcut existing.