<script>
window.dataLayer = window.dataLayer || [];
dataLayer.push({
    event : 'login', // name of the event (always the same)
    userId : 'abc123', // the id of the user (stored in a database)
    pricingPlan : 'premium', //the pricing plan of a visitor (inserted dynamically)
    sessionNumber : 7 //the number of the session of the logged in user
});
</script>