How to create access of child applications to the parent application with API?

Question

API

All applications are on different domains and take data from the parent application using Ajax requests. How is this process usually organized?
Or for example there is a service type application. A person registers, receives a role for example Champion, and can only receive data from a specific page of the parent application such as www.parent/champion/post2 etc.
Maybe there are some libraries or just materials on how to organize it.

Answer 1

you want to learn about microservices.