Gadget server and personalisation

I want to create a portal that attracts users from the gadgets into web pages and is also used as central place to access our sites that they are subscribed to. I need to pass through to those sites an XML file with all the user's preferences so that the site can personalise the experience and remember things form last session, etc. Using the built-in SSO, can I pass in this XML file? Can I point the SSO at a SQL database instead? or is it best to just copy credentials into LDAPS How easy it is to connect up another SSO such as CAS? Many thanks in advance for any help