public function authenticateAsAccount($account, $key, $tenantId = NULL, $tenantName = NULL) {
    $ops = array(
      'apiAccessKeyCredentials' => array(
        'accessKey' => $account,
        'secretKey' => $key,
      ),
    );

    if (!empty($tenantId)) {
      $ops['tenantId'] = $tenantId;
    }
    elseif (!empty($tenantName)) {
      $ops['tenantName'] = $tenantName;
    }

    return $this->authenticate($ops);
  }