code: def basic_auth_tween_factory(handler, registry):
      
      def basic_auth_tween(request):
          remote_user = get_remote_user(request)
          if remote_user is not None:
              request.environ['REMOTE_USER'] = remote_user[0]
          return handler(request)
      return basic_auth_tween
docs: Do basic authentication, parse HTTP_AUTHORIZATION and set remote_user
      variable to request