protected function getAccessTokenOptions(array $params)
    {
        // Add params that are required
        $params += [
            'scope' => implode($this->getScopeSeparator(), $this->getDefaultScopes()),
        ];

        $options = parent::getAccessTokenOptions($params);

        // Add authorization header
        $options['headers']['Authorization'] = sprintf(
            'Basic %s',
            base64_encode(
                sprintf(
                    '%s:%s',
                    $this->clientId,
                    $this->lif
                )
            )
        );

        return $options;
    }