How to get/display Current logged-in User name in Dynamics CRM Portal

How to get/display Current logged-in User name in CRM Portal

This is generic requirement to say welcome message to the logged-in user on any portal.If portal user is logged-in user it will show their name and if not will show as guest user.

{% if user %}

  Hello, {{ user.lastname }}!

{% else %}

Welcome Guest{{user.anonymous}}!

{% endif %}