On PHPMaster.com today there's a new tutorial posted (from Martin Psinas) about using role-based access controls in PHP-based applications. His method isn't based in any specific framework, so it's easily portable to just about any app out there.

In this article I will discuss my personal favorite approach: role based access control (RBAC). RBAC is a model in which roles are created for various job functions, and permissions to perform certain operations are then tied to roles. A user can be assigned one or multiple roles which restricts their system access to the permissions for which they have been authorized.

He starts with a warning that, if not properly maintained, a role-based system like this can get to be somewhat chaotic so a rules should be in place around the adding and removing of permissions at certain times. His functionality is based on a few database tables - roles, permissions and cross-reference tables between users/roles & permissions/roles. All of the code you'll need to implement the system is included in a Role class, the PrivilegedUser class and the methods you'll need to add/remove/check the logged in user's permissions.