code: def new_csrf_token(self, session_key):
          
          try:
              csrf_token = self._generate_csrf_token()
  
              session = self._lookup_required_session(session_key)
              session.set_internal_attribute('csrf_token', csrf_token)
              self.session_handler.on_change(session)
  
          except AttributeError:
              raise CSRFTokenException('Could not save CSRF_TOKEN to session.')
  
          return csrf_token
docs: :rtype: str
          :returns: a CSRF token