I have added support for enabling Apache's REMOTE_USER support. This is authentication mechanism where apache is configured to do the authentication, and pass the resulting user in REMOTE_USER variable. Please check apache docs to find out how to set the apache config options for the pmwiki directory.
In the process, I have streamlined session management, and we possibly can add support for other mechanisms such as facebook and twitter's oAuth in easy manner.
Please read the README for details and local configuration options and my contact details.