How do you implement dynamic j2ee roles

[lost_traveller]

I have a requirement that the j2ee roles for any given user may change dynamically in any given user session.
I am using container managed security, buy how do I capture JBosses role checking code to call into my following code?:

getMySessionBean().isUserInRole(java.security.Principal);

At the moment JBoss asks for a list of roles for a user when you log on, i.e.

 public Group[] getRoleSets()
 {
 SimpleGroup callerPrincipal = new SimpleGroup("CallerPrincipal");
 callerPrincipal.addMember(identity);
 SimpleGroup s = new SimpleGroup("Roles");
 s.addMember(new SimplePrincipal("a.j2ee.role"));
 s.addMember(new SimplePrincipal("b.j2ee.role"));
 return new Group[] { s, callerPrincipal};
 }

But I want to be able to calculate if a user has a given role at runtime using my own isUserInRole(Principal) method?

Thanks in advance.