On the process of setting up a [apache2] reverse proxy, it can happen that one needs to set a RequestHeader depending on some conditions. It seems that, though the "Header" directive accepts an env var as condition, this cannot be used with "RequestHeader", which seems to be a "missing" feature, at least in the case of a Reverse Proxy. This is irrelevant for 1.3, as "RequestHeader" is new in 2.0
Created attachment 10995 [details] Patch against modules/metadata/mod_headers.c
Created attachment 10996 [details] Suggested documentation update if patch is accepted.
Thanks. I've committed the change to HEAD (which your patch wasn't against, so I've modified it to match ;).