Best way to use an existing User model with this gem?

Hi,

I have an app with an existing User model. Users can have Roles, one of the Roles is "admin". Users are authenticated with SSO and that's all working nicely.

What I'd like to do is have administration-zero use this existing model instead of Admin::User, and allow users to view the admin UI if they have the "admin" Role.

Any thoughts on how I could do this?