private function validateAccessList() {
        // Get all user lists
        $declaredPublicKeys = array_map(function($acl) {
            return $acl['publicKey'];
        }, $this->accessList);

        $publicKeys = [];
        foreach ($declaredPublicKeys as $key) {
            if (in_array($key, $publicKeys)) {
                throw new InvalidArgumentException('Public key declared twice in config: ' . $key, 500);
            }

            $publicKeys[] = $key;
        }
    }