Authentication

You're working on a security system for a top-secret organization. The system is designed to be as simple as possible - a basic username and password access. But the organization needs an extra layer of security - the system should throw a custom AuthenticationError if the username and password provided by the user do not match the predefined values. You need to create a program to handle this situation.

In this exercise, the predefined username is admin and the password is password123. These are hardcoded into the program and cannot be changed.

Create a function def auth(username, password): that would perform the checks and return True if the access is granted.