public function setProtectionPolicy($protectionPolicy)
    {
        if ($protectionPolicy !== GuardInterface::POLICY_ALLOW && $protectionPolicy !== GuardInterface::POLICY_DENY) {
            throw new Exception\RuntimeException(sprintf(
                'An invalid protection policy was set. Can only be "deny" or "allow", "%s" given',
                $protectionPolicy
            ));
        }

        $this->protectionPolicy = (string) $protectionPolicy;
    }