What does this extension do, and how does it work?

The part with autologin

This plugin is intended to be used for cases where a front-end login is required for certain parts of the process (e.g., signing up for a course) using the seminars extension, but where users should be allowed to enter their personal data without having to go through the process of creating a front-end user account.

Technically, the extension provides a form for the user to enter their data. It then creates a new front-end user account for the user with an autogenerated username and password. The user is then automatically logged in and redirected to the page provided in the redirect_url GET parameter (the same way the normal front-end login process works).

The onetimeaccount autologin also sets a flag in the user session that allows the seminars extension to recognize a login to be a one-time login and then automatically log the user out again after they have finished signing up for an event.

The onetimeaccount plugin can be used on the login page either next to the normal login form or instead of it.

The part without autologin

This plugin is intended to be used for cases where a having user data is required for certain parts of the process (e.g., signing up for a course) using the seminars extension, but where users should be allowed to enter their personal data without having to go through the process of creating a front-end user account.

Technically, the extension provides a form for the user to enter their data. It then creates a new front-end user account for the user with an autogenerated username and password. The UID of the newly-created user then will be stored in the session, allowing the seminars registration form to recognize that the use has provided their data. (The FE user will not be auto-logged in, though.) The user is then automatically redirected to the page provided in the redirect_url GET parameter (the same way the normal front-end login process works).

The onetimeaccount plugin can be used on the login page either next to the normal login form or instead of it (if a FE login is not relevant).