That’s heavily under construction (don’t expect it to be “fun” until late 2024) ; but if you’re interested in tech details, check out Backpack https://github.com/Vrixyz/backpack
Players can have an account created on Backpack server when playing games supporting Backpack (game developers must integrate it).
For the moment Backpack supports (in tech demo) accounts through email/password, but later on I’d like to support facebook and your favorite way of authenticating (private key, github, twitter…)