The Number of web sites and services in our daily duties grows from year to year. Each service requires standard user authentication. Generally, Application Security started with login/password pair, for all of us. It’s not easy to remember even dozen strong passwords, particularly if some service is used once per month. Keep in mind, we have to use different passwords. Usage of the same password for many web sites is the most worst thing a user can do at line of Application Security.
OpenID vs. Login/password schema
Modern web sites nowadays uses third-party authentication based on OpenID technology