What do you recommend to add authentication to a unity project?

I want to maintain a database. I do not need personal data like email, just keep an inventory associated with a user ID.

The YouTube channel Brackeys does a really great FPS tutorial series that covers this topic. The game creation series is called “Making a Multiplayer FPS in Unity”. The episode that you will want to take a look at is Episode 23, or “User Accounts”. Go check out his channel and go to his playlists. If you scroll down, you should be able to find it. He uses a free database asset (but you can implement your own SQL database if you need it) on the Asset Store, but it’s great for learning the basics of database storage.

Hope I was able to help!