    async def default_handle_logout(self):
        """The default logout action

        Optionally cleans up servers, clears cookies, increments logout counter
        Cleaning up servers can be prevented by setting shutdown_on_logout to
        False.
        """
        user = self.current_user
        if user:
            if self.shutdown_on_logout:
                await self._shutdown_servers(user)

            self._backend_logout_cleanup(user.name)
The default logout action

Optionally cleans up servers, clears cookies, increments logout counter
Cleaning up servers can be prevented by setting shutdown_on_logout to
False.
jupyterhub/handlers/login.py