code: def sign_out(self, redirect_url=None):
      
      config = config_lib.get_config()
      key = self.handler.app.config['webapp2_extras.sessions']['secret_key']
      if redirect_url is None:
        redirect_url = self.handler.request.url
      user_id = self.handler.me.user_id()
      token = xsrfutil.generate_token(key, user_id, action_id=redirect_url)
      return '{}/signout?{}'.format(config['airlock_path'], urllib.urlencode({
          'redirect': redirect_url,
          'token': token,
      }))
docs: Returns a signed URL to disassociate the ouath2 user from the session.