private function parseConditions(DOMElement $xml) : void
    {
        /** @var \DOMElement[] $conditions */
        $conditions = Utils::xpQuery($xml, './saml_assertion:Conditions');
        if (empty($conditions)) {
            /* No <saml:Conditions> node. */

            return;
        } elseif (count($conditions) > 1) {
            throw new \Exception('More than one <saml:Conditions> in <saml:Assertion>.');
        }
        $conditions = $conditions[0];

        if ($conditions->hasAttribute('NotBefore')) {
            $notBefore = Utils::xsDateTimeToTimestamp($conditions->getAttribute('NotBefore'));
            if ($this->getNotBefore() === null || $this->getNotBefore() < $notBefore) {
                $this->setNotBefore($notBefore);
            }
        }
        if ($conditions->hasAttribute('NotOnOrAfter')) {
            $notOnOrAfter = Utils::xsDateTimeToTimestamp($conditions->getAttribute('NotOnOrAfter'));
            if ($this->getNotOnOrAfter() === null || $this->getNotOnOrAfter() > $notOnOrAfter) {
                $this->setNotOnOrAfter($notOnOrAfter);
            }
        }

        foreach ($conditions->childNodes as $node) {
            if (!$node instanceof DOMElement) {
                continue;
            }
            if ($node->namespaceURI !== Constants::NS_SAML) {
                throw new \Exception('Unknown namespace of condition: '.var_export($node->namespaceURI, true));
            }
            switch ($node->localName) {
                case 'AudienceRestriction':
                    $audiences = Utils::extractStrings($node, Constants::NS_SAML, 'Audience');
                    if ($this->validAudiences === null) {
                        /* The first (and probably last) AudienceRestriction element. */
                        $this->validAudiences = $audiences;
                    } else {
                        /*
                         * The set of AudienceRestriction are ANDed together, so we need
                         * the subset that are present in all of them.
                         */
                        $this->validAudiences = array_intersect($this->validAudiences, $audiences);
                    }
                    break;
                case 'OneTimeUse':
                    /* Currently ignored. */
                    break;
                case 'ProxyRestriction':
                    /* Currently ignored. */
                    break;
                default:
                    throw new \Exception('Unknown condition: '.var_export($node->localName, true));
            }
        }
    }