SAML2\Assertion::parseAuthnContext PHP Method

    private function parseAuthnContext(\DOMElement $authnStatementEl)
    {
        // Get the AuthnContext element
        $authnContexts = Utils::xpQuery($authnStatementEl, './saml_assertion:AuthnContext');
        if (count($authnContexts) > 1) {
            throw new \Exception('More than one <saml:AuthnContext> in <saml:AuthnStatement>.');
        } elseif (empty($authnContexts)) {
            throw new \Exception('Missing required <saml:AuthnContext> in <saml:AuthnStatement>.');
        }
        $authnContextEl = $authnContexts[0];
        // Get the AuthnContextDeclRef (if available)
        $authnContextDeclRefs = Utils::xpQuery($authnContextEl, './saml_assertion:AuthnContextDeclRef');
        if (count($authnContextDeclRefs) > 1) {
            throw new \Exception('More than one <saml:AuthnContextDeclRef> found?');
        } elseif (count($authnContextDeclRefs) === 1) {
            $this->setAuthnContextDeclRef(trim($authnContextDeclRefs[0]->textContent));
        }
        // Get the AuthnContextDecl (if available)
        $authnContextDecls = Utils::xpQuery($authnContextEl, './saml_assertion:AuthnContextDecl');
        if (count($authnContextDecls) > 1) {
            throw new \Exception('More than one <saml:AuthnContextDecl> found?');
        } elseif (count($authnContextDecls) === 1) {
            $this->setAuthnContextDecl(new Chunk($authnContextDecls[0]));
        }
        // Get the AuthnContextClassRef (if available)
        $authnContextClassRefs = Utils::xpQuery($authnContextEl, './saml_assertion:AuthnContextClassRef');
        if (count($authnContextClassRefs) > 1) {
            throw new \Exception('More than one <saml:AuthnContextClassRef> in <saml:AuthnContext>.');
        } elseif (count($authnContextClassRefs) === 1) {
            $this->setAuthnContextClassRef(trim($authnContextClassRefs[0]->textContent));
        }
        // Constraint from XSD: MUST have one of the three
        if (empty($this->authnContextClassRef) && empty($this->authnContextDecl) && empty($this->authnContextDeclRef)) {
            throw new \Exception('Missing either <saml:AuthnContextClassRef> or <saml:AuthnContextDeclRef> or <saml:AuthnContextDecl>');
        }
        $this->AuthenticatingAuthority = Utils::extractStrings($authnContextEl, Constants::NS_SAML, 'AuthenticatingAuthority');
    }