text: from django.db import connection
  from django.contrib.auth.models import User, Permission
  from django.contrib.auth.backends import RemoteUserBackend
  
  class ShibbolethRemoteUserBackend(RemoteUserBackend):
      """
      This backend is to be used in conjunction with the ``RemoteUserMiddleware``
      found in the middleware module of this package, and is used when the server
      is handling authentication outside of Django.
  
      By default, the ``authenticate`` method creates ``User`` objects for
      usernames that don't already exist in the database.  Subclasses can disable
      this behavior by setting the ``create_unknown_user`` attribute to
      ``False``.
      """
  
      # Create a User object if not already in the database?
      create_unknown_user = True
  
      def authenticate(self, remote_user, shib_meta):
          """
          The username passed as ``remote_user`` is considered trusted.  This
          method simply returns the ``User`` object with the given username,
          creating a new ``User`` object if ``create_unknown_user`` is ``True``.
  
          Returns None if ``create_unknown_user`` is ``False`` and a ``User``
          object with the given username is not found in the database.
          """
          if not remote_user:
              return
          user = None
          username = self.clean_username(remote_user)
          shib_user_params = dict([(k, shib_meta[k]) for k in User._meta.get_all_field_names() if k in shib_meta])
          # Note that this could be accomplished in one try-except clause, but
          # instead we use get_or_create when creating unknown users since it has
          # built-in safeguards for multiple threads.
          if self.create_unknown_user:
              user, created = User.objects.get_or_create(username=username, defaults=shib_user_params)
              if created:
                  user = self.configure_user(user)
          else:
              try:
                  user = User.objects.get(**shib_user_params)
              except User.DoesNotExist:
                  pass
          return user
  