Thank you guys for your answers. I already do that (copying email in username field) but copying data in database and having an extra step is not satifactory, especially when you have many users to manage!
As users always remember their email, not their username, my question is: whatever the username, is there a way to make RS use the email field instead of the username field to log in?
it is now the best practice in authentification system, in Moodle for instance, it is possible to activate it as an option:
Maybe an idea to integrate this feature for the future roadmap via config or a new plugin... I have reported my request to Dan Huby for info.
BR