I am wondering on how a microservices communication and data modeling would go on. It is a nodejs-mongodb, part of self-learning. I am seeing they need separate repos.

In Core service, I have Client document model storing user phone and password.

in Reporting service, I want to use Client. I have a ReportRequest model that i need to relate to Client defined in core service. Given they are independent services.

how would I go about creating the relationship? Also how do the two services communication, mainly for Reporting service to know if a user is logged in or not.