The purpose of authentication is to determine if a user can access the system with the provided credentials of user ID and password, while authorization determines what a user can do once they are inside the system. You should create a centralized system to manage your user's authentication and authorization.
This centralized user management system helps you to keep track of the user's activity so you can deactivate them if they are no longer a part of the system. You can define standard rules to onboard a new user and remove access for inactive users. The centralized system eliminates reliance on long-term credentials and allows you to configure other security methods such as password rotation and strength.
For authorization, you should start with the principle of least privilege—it means users should not have any access to begin with, and then begin assigning them only the required access according to their job role...