Merge branch 'federated-login-service'

* federated-login-service:
  show a message indicating why they are seeing the login screen
  extend from RuntimeException to simplify tunneling
  Oops
  honor UserPropertyDescriptor.isEnabled()
  relaxing this a bit
  report the user that was signed in.
  Added the registration screen for newly identified user.
  unclaimed identity should commence a signup sequence
  tweaking abstraction
  needs a title
  Added an extension point for external federated login service.
  still a work in progress. Federated login support