'Refreshes the access token.
Skip all the storage hoops and just refresh using the API.
Args:
http: an object to be used to make HTTP requests.
Raises:
HttpAccessTokenRefreshError: When the refresh fails.'

def _refresh(self, http):

    try:
        self._retrieve_info(http)
        (self.access_token, self.token_expiry) = _metadata.get_token(http, service_account=self.service_account_email)
    except http_client.HTTPException as err:
        raise client.HttpAccessTokenRefreshError(str(err))
