Dynamics 365 Portal Profile Validation

Hi All,

I am using the Out of the box Profile Page in the Dynamics 365 Portals. I only changed the CRM form behind to add some other fields (from Contact entity).

By default, Name (First and Last) are mandatory, there is already validation. However, I do not see any way to add (by configuration) some other validations. Example: I have Postal code field, which I want to be validated. 

Profile page uses a Page Template of type Rewrite, there is no entity form behind where I could configure the validations. 

How can I add custom validations to the Profile ? 

Thank you.