Caseyland

Does anyone know how to get the proper .ics address for your Google Calendar contacts’ birthday calendar?  It doesn’t seem to be http://www.google.com/calendar/ical/%23contacts@group.v.calendar.google.com/public/basic.ics, as that doesn’t allow for any identification of whose calendar I’m looking for. Passing login credentials doesn’t seem to do it.  So, /ical/casey/public/basic.ics?  Something else?