Java Development Tools

I am currently working on the design of a new application. This application will have the following oracle tables to manage users, roles and privileges;

user has one to many roles
e.g. user1 is a clerk and a supervisor
a role has one to many privileges
e.g. a clerk can create and query records, a supervisor can delete records

If I were to use hibernate 3.0 as the persistence layer across the top of my oracle database, what would be the best way to;

a) develop the login functionality
b) manage the user's roles and privileges to enable/disable appropriate functionality within the application, given that the user will have the ability to change both a users roles, and a roles privileges within the application?

Thanks in advance for your thoughts/advice

David