Hace poco he tenido un problema con redirecciones SSL en apache
[warn] proxy: No protocol handler was valid for the URL $URL. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.
Tras bajar el nivel de log a debug pude ver mensajes de este tipo:
[debug] proxy_util.c(1354): [$IP] proxy: *: found reverse proxy worker for https://$URL
[debug] mod_proxy.c(756): Running scheme https handler (attempt 0)
[debug] mod_proxy_http.c(1643): proxy: HTTPS: declining URL https://$URL (mod_ssl not configured?)
[debug] mod_proxy_ajp.c(492): proxy: AJP: declining URL https://$URL
[debug] mod_proxy_ftp.c(798): proxy: FTP: declining URL https://$URL – not ftp:
[debug] mod_proxy_connect.c(100): proxy: CONNECT: declining URL https://$URL
[warn] proxy: No protocol handler was valid for the URL $URL. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.
Tras consultar la documentación de apache sobre ssl(http://httpd.apache.org/docs/2.0/mod/mod_ssl.html) y varios documentos relacionados uno aprende que para poder hacer redirecciones proxies de urls https es necesario que nuestro apache tenga soporte para ssl y activar el parametro SSLProxyEngine.