As a Kaa developer, I want to be able to aggregate multiple endpoints (potentially across several applications) under a single "user" entity, thus modeling endpoint ownership and enabling interactions across the endpoints that belong to the same user.
Aggregation may be based on the external log-in information (Facebook, G+, etc.).
Within the scope of this story Kaa must support custom endpoint user verification strategies that would be assignable per application. In order to log in with a specific user, Kaa endpoint would have to supply the server with the external system's user ID and authentication token. Endpoint user verification strategy is responsible for confirming the user registration against the external authentication system.