Context should contain information which is required to get
the information if the service call is authenticated. Context
could be the username for example. But services call other
services internally and for this, authentication must not be
checked. In this case, they can now pass Authentication::Full
which always successfully authenticates.
App devices which implementation will be used. For now,
the types of the implementations must be defined manually.
This is requied because the State in the REST endpoints must
contain a type which can provide all services.
