- The ``RemoteUserAuthenticationPolicy ``, ``AuthTktAuthenticationPolicy``,
  and ``SessionAuthenticationPolicy`` constructors now accept an additional
  keyword argument named ``debug``.  By default, this keyword argument is
  ``False``.  When it is ``True``, debug information will be sent to the
  Pyramid debug logger (usually on stderr) when the ``authenticated_userid``
  or ``effective_principals`` method is called on any of these policies.  The
  output produced can be useful when trying to diagnose
  authentication-related problems.