+ $headers = $this->requestStack->getCurrentRequest()->headers->all();
+ // Order headers by name to have less cache variations.
+ ksort($headers);
+ $result = '';
+ foreach ($headers as $name => $value) {
+ if ($result) {
+ $result .= '&';
+ }
+ // Sort values to minimize cache variations.
+ sort($value);
+ $result .= $name . '=' . implode(',', $value);
+ }
+ return $result;