Whenever you use mod_proxy you need to make sure that your server will not become a proxy for freeriders. Allowing clients to issue proxy requests is controlled by the ProxyRequests directive. Its default setting is Off, which means proxy requests are handled only if generated internally (by ProxyPass or RewriteRule...[P] directives). Do not use the ProxyRequests directive on your reverse proxy servers.
Eric Cholet (Logilune) and
Stas Bekman (StasoSphere & Free Books).