I think the best you can hope for using Cake native ACL implementation is as follows:
cake acl create aro root public cake acl create aro root registered cake acl create aro registered administrators (create acos using AclExtras) cake acl grant registered controllers cake acl grant public controllers cake acl deny public controllers/MySecureController cake acl deny public controllers/Widgets update cake acl deny public controllers/Widgets delete
(above everything is done through the shell of the cake, but it is easily translated into a version of PHP)
Basically, you can use the default paradigm (as shown in the Cake tutorial on your own ACL) or the default paradigm as described above. Whichever method you choose will depend on how you expect the application to grow: whether most of your controllers will be publicly available with only a few select, restricted administrators, or whether most of your application will be limited to public specific access where it is is it necessary? In any case, you still need to grant or deny access.
Note the two AROs created in root : public and registered . Using this model, process the registered one as if it were root when creating your ARO tree - put all your "real user" groups under it. Thus, you can use the ACL as usual for objects under the registered , and public users will exist outside this.
All that said, nothing prevents you from using Cake authentication mechanism and minimizing your own access control method. Here is an example: Simple authentication and authorization . (NOTE: This is written for CakePHP 2.0, but concepts also apply to 1.3).
EDIT -
After reading the question and other answers again, I realized that you are more focused on the role-based access control model, rather than on the traditional model of the built-in ACL component for each user. Here are some examples of the auth built-in extension for RBAC:
Role Based ACLs in CakePHP
CakePHP Auth Component: Users, Groups, Permissions
In addition, this two-part article describes a database-based role-based authorization approach that can be applied to your Cake application.