How does one go about putting multiple instances of the same application, on
the same server, each with it's own user registry?

I understand that for an in house implementation, with many different apps
on the same server, it makes sense to enable Global Security and make each
app use the same user registry for authentication. (Local OS or LDAP for
example.)

But when hosting the same app (in many different instances on the same
server), and that each instance represents a seperate "hosted client" with
it's own unique user base, how does one have each app connect to it's own
user registry?

The app I am refering to (that is hosted in multiple instances on the same
server), has it's own user registry in a back end datastore that is in a one
to one configuration with each app instance. In addition we want the "super
user" of each app instance to administer the user registry of the app
instance and not have to store all users, for all the app instances, in a
one central location, where a WAS admin may be forced to administer the user
credentials fro each client's user base.

We want to leverage the J2EE security using JAAS and a custom user
repository but on a per app instance basis and not on a per server instance.

Any light shed on this topic would be greatly appreciated.