SimpleSAML_Utilities::checkURLAllowed PHP Method

    public static function checkURLAllowed($url, array $trustedSites = null)
    {
        return \SimpleSAML\Utils\HTTP::checkURLAllowed($url, $trustedSites);
    }

    /**
     * Initialize the filter.
     *
     * @param array $config  Configuration information about this filter.
     * @param mixed $reserved  For future use
     */
    public function __construct($config, $reserved)
    {
        parent::__construct($config, $reserved);
        assert('is_array($config)');
        if (array_key_exists('enforce_2fa', $config)) {
            $this->enforce_2fa = $config['enforce_2fa'];
            if (!is_bool($this->enforce_2fa)) {
                throw new Exception('Invalid attribute name given to simpletotp::2fa filter:
 enforce_2fa must be a boolean.');
            }
        }
        if (array_key_exists('secret_attr', $config)) {
            $this->secret_attr = $config['secret_attr'];
            if (!is_string($this->secret_attr)) {
                throw new Exception('Invalid attribute name given to simpletotp::2fa filter:
 secret_attr must be a string');
            }
        }
        if (array_key_exists('not_configured_url', $config)) {
            $this->not_configured_url = $config['not_configured_url'];
            if (!is_string($config['not_configured_url'])) {
                throw new Exception('Invalid attribute value given to simpletotp::2fa filter:
 not_configured_url must be a string');
            }
            //validate URL to ensure it's we will be able to redirect to
            $this->not_configured_url = SimpleSAML_Utilities::checkURLAllowed($config['not_configured_url']);
        }
    }