Bitpay\Config\Configuration::addKeyStorageNode PHP Метод

    protected function addKeyStorageNode()
    {
        $builder = new TreeBuilder();
        $node = $builder->root('key_storage', 'scalar');
        $node->info('Class that is used to store your keys')->defaultValue('Bitpay\\Storage\\EncryptedFilesystemStorage')->validate()->always()->then(function ($value) {
            if (!class_exists($value)) {
                throw new \Exception(sprintf('Could not find class "%s".', $value));
            }
            // requires PHP >= 5.3.7
            if (!is_subclass_of($value, 'Bitpay\\Storage\\StorageInterface')) {
                throw new \Exception(sprintf('"%s" does not implement "Bitpay\\Storage\\StorageInterface"', $value));
            }
            return $value;
        })->end();
        return $node;
    }