<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 session of the logged in user
});
</script>