At the time of this writing, libwww v5.6 seems to proxy https requests fine with an Apache mod_proxy server. It sends a line like:

  GET https://www.nodeworks.com HTTP/1.1

to the proxy server, which is not the CONNECT request that some proxies would expect, so this may not work with other proxy servers than mod_proxy. The CONNECT method is used by Crypt::SSLeay's internal proxy support.