<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def refresh(self):
 """ Refresh the access token """

        data = {
            'grant_type': 'refresh_token',
            'refresh_token': self._token.refresh_token
        }

        response = self.http_client.post(self.URL, data=data, auth=(self.client_id, self.client_secret))
        response.raise_for_status()
        self._token = Token.from_json(response.json())