SAML2\Assertion::parseSignature PHP Method

    private function parseSignature(\DOMElement $xml)
    {
        /** @var null|\DOMAttr $signatureMethod */
        $signatureMethod = Utils::xpQuery($xml, './ds:Signature/ds:SignedInfo/ds:SignatureMethod/@Algorithm');
        /* Validate the signature element of the message. */
        $sig = Utils::validateElement($xml);
        if ($sig !== false) {
            $this->wasSignedAtConstruction = true;
            $this->certificates = $sig['Certificates'];
            $this->signatureData = $sig;
            $this->signatureMethod = $signatureMethod[0]->value;
        }
    }