code: def expose(policy):
      
      def wrapper(func):
          func.mitogen_service__policies = (
              [policy] +
              getattr(func, 'mitogen_service__policies', [])
          )
          return func
      return wrapper
docs: Annotate a method to permit access to contexts matching an authorization
      policy. The annotation may be specified multiple times. Methods lacking any
      authorization policy are not accessible.
  
      ::
  
          @mitogen.service.expose(policy=mitogen.service.AllowParents())
          def unsafe_operation(self):
              ...
  
      :param mitogen.service.Policy policy:
          The policy to require.