Can't really help you out with the authentication part though, although having a search through http://www.macosxhints.com is highly recommended.
You can authenticate using LDAP I believe, I'm not certain... I've not tried
it. OSX definately has some Kerberos support out of the box though.
You can also get the source code for netinfo (the Darwin/OSX directory service) from the Darwin project, and it has been ported to linux at least
once in the past...
One of the first hits in Google for "Mac OS X Ldap"
Authenticating and Authorizing Mac OS X Users http://clc.its.psu.edu/Labs/Mac/resources/authdoc/default.aspx
Seems to cover ldap and kerberos. -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
