I have a portal application that loads external content (widgets) via an iframe. Users login to CAS via the portal itself. There are a few portal APIs, though, that need to be called from that external content. What information do I have to pass from the portal to the widgets that the widgets can use to make these calls without being rejected by CAS?

UPDATE

The more I investigate, the more I think that my question boils down to how CAS actually does what it's supposed to do. In other words, how can I go from one site where I've authenticated to another and tell it that I've already done the authentication thing. What's the mechanism behind that and how can I employ in in a web context.