How to implement a specific user authentication process for a Unity game?

I have developed a game using Unity and I want to restrict the distribution of my game to only specific users, between 10 to 24, to prevent unauthorized access and piracy. I am planning to implement an authentication process for my game with the following steps:

1: Upon installation, the game generates a unique ID and prompts the user to enter their username.

2:The game sends a request to my server with the generated ID and the user’s entered username for verification.

3:If the user’s ID and username are confirmed, I will manually grant them access by checking the approval box on my server. If the approval box is checked, the game will launch for the user. If the approval box is unchecked, the user will see a pending page, indicating that their access request is still being processed.

However, I am unsure how to practically implement steps two and three of my proposed authentication process. Can anyone provide me with guidance or recommendations on how to implement this specific authentication process for a Unity game? I would also appreciate any alternative authentication methods that can help me achieve my goal of restricting access to specific users.

Thank you in advance for your help and expertise.