Contao\CoreBundle\Framework\ContaoFramework::initializeLegacySessionAccess PHP Method

    private function initializeLegacySessionAccess()
    {
        if (!$this->session->isStarted()) {
            return;
        }
        $_SESSION['BE_DATA'] = $this->session->getBag('contao_backend');
        $_SESSION['FE_DATA'] = $this->session->getBag('contao_frontend');
    }