OpenID is an open, decentralized standard for authenticating users. It is currently being used by popular websites like Google, Yahoo!, MySpace, Flickr and many more. Logon credentials used on all of these sites can be used to log on to your Kentico CMS site.
OpenID is the easiest to use of the three supported third-party authentication services. For it to work on your site, you don't need to register your site, all you need to do is take the following two steps:
1. Set up Kentico CMS for OpenID authentication - learn here
2. Use one of the OpenID web parts on any page of your site - info here
The following diagram shows how the process of OpenID login works: