How to connect the user's domain to the site pages?

Question

Domain Name System

On example.com, the user can create the page page1.example.com.

The goal is for him to be able to add his own userdomain.com, which will render the page page1.example.com.

I understand that you need to raise your dns server? If yes, how and what to do?

PS example.com is protected by cloudflare and requests go through nginx

Answer 1

To "add" userdomain.com, that user needs to buy this domain and not from you, but from the registrar. Then assign it to the NS-server in your account (if the account allows several domains) and register alias/redirect.