This class can be used to authenticate users with OpenID single sign-on Web services.
It can set the required and optional user profile fields that the users must provide to authenticate, establish a connection to an OpenID server, redirect the user browser to the OpenID server pages, making the browser be redirected back to a given page when the authentication is finished.
When the user browser is redirected to the site, the class can connect to the OpenID server to verify whether the returned authentication key is valid.