How to use the kerberos.Kerberos function in kerberos

if (!req.headers.authorization) {
        res.set( 'WWW-Authenticate', 'Negotiate' );

        //
        console.log('-----response-----');
        console.log(res._headers);

        res.status(401).send();

    } else {

        // this code is only for Linux !

        var KerberosNative = require('kerberos').Kerberos;
        var kerberos = new KerberosNative();
        var ActiveDirectory = require('activedirectory');
        var ad = new ActiveDirectory({
            "url": "ldap://",
            "baseDN": "",
            "username": "",
            "password": ""});
        //cut phrase "Negotiate "
        var ticket = req.headers.authorization.substring(10);

        //init context
        kerberos.authGSSServerInit("HTTP", function(err, context) {
            //check ticket
            kerberos.authGSSServerStep(context, ticket, function(err) {
                //in success context contains username
                ad.findUser(context.username, function(err, user) {
                    //get user groups