I'd hook up my PGP key. Or X.509 certificate. Or old good username and password pair. Something I can truly own and handle. Why do I need some third party to have an identity?

Then I'd enlist accounts with any imaginable third parties (email addresses, Facebook, VKontakte, Google+, BitCoin addresses, GitHub, BitBucket, StackOverflow and so on and so on) as something I have at the moment.