For a more up-to-date example of how to use LoopBack 3 with multi-user roles please check codekeyz/loopback-multirole-api-starter.
Example project to show a new feature in LoopBack 3.3.0: Access Control with multiple user models
Read more about this feature here: http://loopback.io/doc/en/lb3/Authentication-authorization-and-permissions.html#access-control-with-multiple-user-models