The Zend_Auth_Adapter_OpenId adapter can be used to authenticate users using remote OpenID servers. This authentication method assumes that the user submits only their OpenID identity to the web application. They are then redirected to their OpenID provider to prove identity ownership using a password or some other method. This password is never provided to the web application.

The OpenID identity is just a URI that points to a web site with information about a user, along with special tags that describes which server to use and which identity to submit there. You can read more about OpenID at the OpenID official site.

The Zend_Auth_Adapter_OpenId class wraps the Zend_OpenId_Consumer component, which implements the OpenID authentication protocol itself.