How do users authenticate? Do they need to register for an account and give their email address to every website they want to comment on? This seems like it w

How do users authenticate? Do they need to register for an account and give their email address to every website they want to comment on? This seems like it would have been a good use-case for Persona, but that project was cancelled; is there any good replacement these days, besides the ubiquitous "sign in with your facebook account"?