It should work with also a local version of the task server. you can start a local task server inside your application and use that to interact without the need of using the Mina Server at all..
You can also expose the task server bean as a JNDI resourse so multiple applications can use it if it's needed (it's a common requirement to share the task server across different applicaitons that will be running processes or creating tasks).
Usually what you need to build is a task list oriented UIs. I'm not sure to understand correctly your example. The user that is logged in should see his/her own tasks (or the one belonging to it's group). If you want to see another user tasks you need to loggin with a different user (a common requirement as well).
If you can provide a simple application/test that shows and setup the JEE realm with some mock users we can help you to improve it as long as we can have a generic example like the LDAP one.
Cheers