code: def prepare_filenames(self, normalized_url, request):
          
          filenames = [normalized_url]
          if request.user.is_authenticated():
              filenames.insert(0, normalized_url + ".authenticated")
          else:
              filenames.insert(0, normalized_url + ".anonymous")
          return filenames
docs: Prepare template filename list based on the user authenticated state
  
          If user is authenticated user, it use '_authenticated' as a suffix.
          Otherwise it use '_anonymous' as a suffix to produce the template
          filename list. The list include original filename at the end of the
          list.
  
          Args:
              normalized_url (str): A normalized url
              request (instance): An instance of HttpRequest
  
          Returns:
              list
  
          Examples:
              >>> from mock import MagicMock
              >>> request = MagicMock()
              >>> backend = AuthTemplateFilenameBackend()
              >>> request.user.is_authenticated.return_value = True
              >>> filenames = backend.prepare_filenames('foo/bar/hogehoge',
              ...                                       request)
              >>> assert filenames == [
              ...     'foo/bar/hogehoge_authenticated.html',
              ...     'foo/bar/hogehoge.html'
              ... ]
              >>> request.user.is_authenticated.return_value = False
              >>> filenames = backend.prepare_filenames('foo/bar/hogehoge',
              ...                                       request)
              >>> assert filenames == [
              ...     'foo/bar/hogehoge_anonymous.html',
              ...     'foo/bar/hogehoge.html'
              ... ]
              >>> request.user.is_authenticated.return_value = True
              >>> filenames = backend.prepare_filenames('',
              ...                                       request)
              >>> assert filenames == [
              ...     'index_authenticated.html',
              ...     'index.html'
              ... ]
              >>> request.user.is_authenticated.return_value = False
              >>> filenames = backend.prepare_filenames('',
              ...                                       request)
              >>> assert filenames == [
              ...     'index_anonymous.html',
              ...     'index.html'
              ... ]