As a good extension it might be helpfull for Piwik-Administrators to have a plugin called ‘User Registration’.
This plugin allows User to register for Piwik-instance with their Mail Adress, User Name etc. The admin will receive an automatic mail with a simple Link to Piwik. There, he can approve membership and add required fields like Profile etc. and click simply on “save”.
It’s time consuming registering new User if your system is used by many users.