Implement a "get my own ressources" authentication/authorization backend

[boblefrag]

We need to be able to show to a user only his own ressources. Authentication and datastore should be able to comunicate.

This should be flexible enough to offer a way to user-limit the ressources per HTTP method (GET, POST, PUT ...)

[boblefrag]

On option should be to add a special filter when authenticating. Like:

 {"filters": "restrict_ressource": "<username>"}.

When the datastore call filter, it should be able to use this filter to restrict ressources to the one belonging to the user