[Zope] SSO using Zope?

I've been evaluating Zope as a possible corporate portal server for my company. I'm currently working on tying it to our existing directories via LDAP and have been very impressed. One feature I have not been able to find any reference re: Zope is SSO. (single sign-on) one of the primary uses of this portal would be the ability for my user's to sign in once and have the portal then pass their credentials on to external pages. Have there been any attempts at this using Zope? I've scoured the web sights, and the one book (Zope Bible) that I have. I'd like to know that what I need is possible/practicle using Zope before I devote too much more effort. Any pointers/URL links/RTFM page 243 comments would be most welcome. --Andrew