Contao\CoreBundle\EventListener\StoreRefererListener::storeBackendReferer PHP Method

    private function storeBackendReferer(Request $request)
    {
        if (!$this->canModifyBackendSession($request)) {
            return;
        }
        $key = $request->query->has('popup') ? 'popupReferer' : 'referer';
        $refererId = $request->attributes->get('_contao_referer_id');
        $referers = $this->prepareBackendReferer($refererId, $this->session->get($key));
        $ref = $request->query->get('ref', '');
        // Move current to last if the referer is in both the URL and the session
        if ('' !== $ref && isset($referers[$ref])) {
            $referers[$refererId]['last'] = $referers[$ref]['current'];
        }
        // Set new current referer
        $referers[$refererId]['current'] = $this->getRelativeRequestUri($request);
        $this->session->set($key, $referers);
    }