Digital Certificates
"A digital certificate is an electronic "credit card" that establishes your credentials when doing business or other transactions on the Web. It is issued by a certification authority (CA). It contains your name, a serial number, expiration dates, a copy of the certificate holder's public key."
"Internet business and many other transactions require a more stringent authentication process [than usernames]. The use of digital certificates issued and verified by a Certificate Authority (CA) as part of a Public Key Infrastructure is considered likely to become the standard way to perform authentication on the Internet." - whatis.com