Filtering/Reducing Menu-Items

I have written my own sitemapprovider in asp.net which (for the time being)
reads all MenuItems from an sql-server table. Now I need to enhance the
functionality to select that part of the nodes depending on the logon
information of the user. So: what is the supposed way to select (and show)
only those nodes via the sitemapprovider to which the user has been granted
access?

Maybe one way: Is there a way the Sitemapprovider can access Session-Vars,
because there I stored the User-Information in the login-process.

Thanks for any help...
Juergen.