OpenID provides sites and services with a decentralized protocol for authenticating users through a wide variety of providers. What this means is that a site integrating OpenID can allow its users to log in using, for example, their Yahoo!, Google, or AOL accounts. Not only can the consuming site avoid having to create a login system itself, but it can also take advantage of the accounts that its users already have, thereby increasing user registration and login rates.
In addition to simple authentication, OpenID also offers a series of extensions through which an OpenID provider can allow sites to obtain a user’s profile information or integrate additional layers of security for the login procedure.
In the sections that follow, we’ll take a closer look at these core elements of the OpenID standard.