ProtectedAssetAdapter.php

<?php

namespace SilverStripe\Assets\Flysystem;

use SilverStripe\Control\Director;
use SilverStripe\Control\Controller;
use SilverStripe\Core\Config\Config;
use SilverStripe\Core\Environment;

class ProtectedAssetAdapter extends AssetAdapter implements ProtectedAdapter
{

    /**
     * Name of default folder to save secure assets in under ASSETS_PATH.
     * This can be bypassed by specifying an absolute filesystem path via
     * the SS_PROTECTED_ASSETS_PATH environment definition.
     *
     * @config
     * @var string
     */
    private static $secure_folder = '.protected';

    private static $server_configuration = [
        'apache' => [
            '.htaccess' => self::class . '_HTAccess'
        ],
        'microsoft-iis' => [
            'web.config' => self::class . '_WebConfig'
        ]
    ];

    protected function findRoot($root)
    {
        // Use explicitly defined path
        if ($root) {
            return parent::findRoot($root);
        }

        // Use environment defined path or default location is under assets
        if ($path = Environment::getEnv('SS_PROTECTED_ASSETS_PATH')) {
            return $path;
        }

        // Default location
        return ASSETS_PATH . '/' . Config::inst()->get(__CLASS__, 'secure_folder');
    }

    /**
     * Provide secure downloadable
     *
     * @param string $path
     * @return string|null
     */
    public function getProtectedUrl($path)
    {
        // Public URLs are handled via a request handler within /assets.
        // If assets are stored locally, then asset paths of protected files should be equivalent.
        return Controller::join_links(Director::baseURL(), ASSETS_DIR, $path);
    }
}