[arvidj]

We use something like this called BankID[1] in Sweden to log in to banks and to several other governemental agencies.

[1] http://www.bankid.com/en/what-is-bankid/

[Zash]

BankID is using pretty standard public key crypto with a custom API. http://wiki.fribid.se/ has some docs on how it works (in swedish).