A digital ID, like someone said below. But people (in the UK at least) go mental about that, despite the government already having all the information anyway. Creating a easy way to securely share that information with a 3rd party for online verification is apparently the work of the devil.

In the real world you turn up in person with a passport, or maybe use snail mail as a way to verify an address which is hard to fake.

Online we have to pretend it is still the internet of the 90s where it's all just chill people having a fun time using their handle...