text: # -*- coding: utf-8 -*-
  
  from __future__ import unicode_literals
  
  from zope.interface import Attribute, Interface
  
  
  class IAuthenticationToken(Interface):
      """Represents an authentication token."""
  
      userid = Attribute("""The userid to which this token was issued.""")
  
      def is_valid(self):
          """Checks token validity (such as expiry date)."""
  