SAML2\Assertion::parseAuthnStatement PHP Method

    private function parseAuthnStatement(\DOMElement $xml)
    {
        $authnStatements = Utils::xpQuery($xml, './saml_assertion:AuthnStatement');
        if (empty($authnStatements)) {
            $this->authnInstant = null;
            return;
        } elseif (count($authnStatements) > 1) {
            throw new \Exception('More than one <saml:AuthnStatement> in <saml:Assertion> not supported.');
        }
        $authnStatement = $authnStatements[0];
        if (!$authnStatement->hasAttribute('AuthnInstant')) {
            throw new \Exception('Missing required AuthnInstant attribute on <saml:AuthnStatement>.');
        }
        $this->authnInstant = Utils::xsDateTimeToTimestamp($authnStatement->getAttribute('AuthnInstant'));
        if ($authnStatement->hasAttribute('SessionNotOnOrAfter')) {
            $this->sessionNotOnOrAfter = Utils::xsDateTimeToTimestamp($authnStatement->getAttribute('SessionNotOnOrAfter'));
        }
        if ($authnStatement->hasAttribute('SessionIndex')) {
            $this->sessionIndex = $authnStatement->getAttribute('SessionIndex');
        }
        $this->parseAuthnContext($authnStatement);
    }