Get FreeRADIUS working with Open Directory users
Take a look at this pkg installer to get a radius server running on your OS X Server.FreeRADIUS will allow you to use your OSXS users for a variety of systems that use radius authentication. For example, using it to provide WPA Enterprise support for Airport Extreme basestations. Another use is to support 802.1x authentication for managed networks.
Andreas documents the proceedure pretty well, but it may take you a bit of effort.