Lighttpd

This enhancement request is a follow-up to #1967.

The "REMOTE_USER" key can't be accessed because it is not created until the proxy_X_get_env call in mod_proxy_backend_X.c.

Attached is a patch that overlays REMOTE_USER in req_env as a key that directly accesses con->authed_user. This is very useful in lua scripts that do things on a per-authed_user basis. Modifying the user also works and is useful for customizing authentication schemes in lua that downstream CGI scripts can inherit via REMOTE_USER.