SessionCacheContext.php

<?php

namespace Drupal\Core\Cache\Context;

use Drupal\Component\Utility\Crypt;

/**
 * Defines the SessionCacheContext service, for "per session" caching.
 *
 * Cache context ID: 'session'.
 */
class SessionCacheContext extends RequestStackCacheContextBase {
    
    /**
     * {@inheritdoc}
     */
    public static function getLabel() {
        return t('Session');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getContext() {
        $request = $this->requestStack
            ->getCurrentRequest();
        if ($request->hasSession()) {
            return Crypt::hashBase64($request->getSession()
                ->getId());
        }
        return 'none';
    }

}