ga - login

// Fire this event each time a user successfully logs in.

<script>
window.dataLayer = window.dataLayer || [];
window.dataLayer.push({
 'event': 'login',
 'login_method': 'email',  //Variable value based on the method used to register, e.g. "email" or "google".
 'user_id': 'asdf1234'  //User ID from your website database.
 });
</script>