20.4. Configuring Authentication and Role Mapping using Login Modules

public class SimplePrincipalGroupRoleMapper implements PrincipalRoleMapper {
   @Override
   public Set<String> principalToRoles(Principal principal) {
      if (principal instanceof SimpleGroup) {
         Enumeration<Principal> members = ((SimpleGroup) principal).members();
         if (members.hasMoreElements()) {
            Set<String> roles = new HashSet<String>();
            while (members.hasMoreElements()) {
               Principal innerPrincipal = members.nextElement();
               if (innerPrincipal instanceof SimplePrincipal) {
                  SimplePrincipal sp = (SimplePrincipal) innerPrincipal;
                  roles.add(sp.getName());
               }
            }
            return roles;
         } 
      }
      return null;
   }
}