[keycloak-user] Keycloak - User registration flow query

Hi Team, I have used keycloak identity provider for my web application for authentication purpose. I have a query related to user registration flow - Validations of attributes like "first name" and several other (say optional or mandatory) on user registration page is on the client or server side ? As far i have checked i can't see any client side validation in "register.ftl" file. Idea is to add some custom attributes and perform some basic validations for them. Thanks, Manisha