In my project I'd like to grant users access to specific parts of the application using the Permission API of PicketLink. However I want that access to be time limited and therefore would like my Permission objects to also contain a field with expiration date and maybe some other fields too. I could do that by simply extending the IdentityPermission but the grantPermission() method of PermissionManager doesn't allow me to specify the type of Permission granted or pass any extra parameters. Is there any way I could achieve my desired result?