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 in- creasing 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.
What makes OpenID so intriguing is the fact that it offers a standard that is fully decentralized from the providers and consumers. This aspect is what allows a single consuming site to allow its users to log in via Yahoo! and Google, while another site may want to allow logins via Blogger or WordPress. Ultimately, it is up to the OpenID consumer (your site or service) to choose what login methods it would like to offer its user base.