concurrent logins

Is it possible to restrict a user to a specified amount of concurrent logins? We provide subscriptions for educational facilities and would like to specify user accounts at:
1 login (no concurrent logins)
3 concurrent logins
500 concurrent logins

You can try the below. I've no idea how well it'll work with CB, but it might do the trick.

extensions.joomla.org/extensions/access-a-security/site-security/login-protection/15932

If not you can try searching for other similar extensions or develop one. It's also possible with CB Auto Actions, but still would require coding in a Code action to check IP address and sessions.

Thanks! We've tried plugins such as the one you referred to, but they're limited in that they allow one login, or unlimited. Others don't work well with CB or check by IP address instead of user name.
I was really hoping CB subs could handle it, but hopefully I'll be able to find a developer to write a plugin for us.

Best approach is a plugin that checks the session database for an existing session. If an active session already exists, delete it, and continue with login. This would logout the previous user. This is the least intrusive to the user themselves (so they don't get stuck waiting for a session to expire) and avoids issues with closing browser without logging out first (which would cause them to wait for session to expire).

This approach is actually extremely simple and could be done with a simple Query action with CB Auto Actions with the after login trigger. It'd take no programming beyond writing the query, which would be as follows.

To explain the query it basically queries the database to delete all sessions except for the newest. This ensures only 1 session can exist at a time. If there is no session Joomla will log them out on next page load so this gives you the 1 login at a time only. It is also note prone to silly username or IP address checking issues.

If you want to allow multiple logins you'd just modify the query as follows to ignore the 3 latest.