One of the more tedious moments in visiting a new website is filling out the registration form. Here at Doc's Music Hall, you do not have to fill out a registration form if you are already a member of Drupal. This capability is called distributed authentication, and Drupal, the software which powers Doc's Music Hall, fully supports it.
Distributed authentication enables a new user to input a username and password into the login box, and immediately be recognized, even if that user never registered at Doc's Music Hall. This works because Drupal knows how to communicate with external registration databases. For example, lets say that new user 'Joe' is already a registered member of Delphi Forums. Drupal informs Joe on registration and login screens that he may login with his Delphi ID instead of registering with Doc's Music Hall. Joe likes that idea, and logs in with a username of firstname.lastname@example.org and his usual Delphi password. Drupal then contacts the remote.delphiforums.com server behind the scenes (usually using XML-RPC, HTTP POST, or SOAP) and asks: "Is the password for user Joe correct?". If Delphi replies yes, then we create a new Doc's Music Hall account for Joe and log him into it. Joe may keep on logging into Doc's Music Hall in the same manner, and he will always be logged into the same account.