"Proposer un événement" form : prevent a not connected member from submitting their event, and encourage them to log in

[agilare]

A lot of users (organizers with an account) use this form, where they need to wait our validation (which comes days after), instead of the appropriate classical add event form (in back-office part), where the event is immediately published.
Often, after proposition, realizing that they have to wait and have made a mistake, they log in and resubmit the event.

An idea : on submit if the field "Votre email" matches an email of 1 user account, reject saving of the event and display a password field in order to login the user at the same time as it adds its event; if email matches several user accounts, display a <select> allowing to choose which account.
A bit like password reset with email.