what is POSIX and how to create POSIX User/group?

POSIX (Portable Operating System Interface) is a set of standard operating system interfaces based on the Unix operating system. The most recent POSIX specifications -- IEEE Std 1003.1-2017 -- defines a standard interface and environment that can be used by an operating system (OS) to provide access to POSIX-compliant applications.

Obtain an Access Token -> Create a Group with POSIX Attributes -> Create a User with POSIX Attributes and Add to Group -> Add POSIX Attributes to Existing Groups -> Add POSIX Attributes to Existing Users -> Verify Endpoints.