/**
* Implements FetchAuthTokenInterface#fetchAuthToken.
*
* @param callable $httpHandler
*
* @return array|void
*/
public function fetchAuthToken(callable $httpHandler = null)
{
$audience = $this->auth->getAudience();
if (empty($audience)) {
return null;
}
$access_token = $this->auth->toJwt();
return array('access_token' => $access_token);
}
