How to get a list of all users assigned to a particular role?

I am using RBAC. For this I am creating an interface to manage all operations/tasks/roles/assignments.

Already created operations, tasks, and roles. Then assigned some roles to some users.

Now I want to show a list of users who have particular role. For example, I would choose "admin" and want to see all users with this role. How can I accomplish this using Yii native API? Currently the only way I see is to implement a model, which doesn't sound right for me. There should be an API to get this info. I might have missed some documentation.

Any help is highly appreciated. Thank you.