This really is web-server-specific.
I just read that the new cherokee version supports LDAP because I was upgrading myself. But this is a feature I do not use.
http://www.alobbs.com/1325/Cherokee_0_6_0_released.html
Either way, you need to set up authentication to FirePlay, and use LDAP as the source. This is a common approach for most webservers.