Anyone of you know about a plugin who creates a unique use key  and send via email to allow the email owner to signup, and don't let anyone with a key to signup?

We're working in a proyect, and we choose to work in Moodle due to its versality, but we had the problem than we don't want our signup process available to public.

Searching a lot I found the plugin Invitation, it's almost perfect for our purposes but it have two drawbacks:

1.  It's not available for Moodle 3.7, where we are working (but fortunately I had edited the code to force the instalation and everything goes smoothy, you can ask me if you need it), and

2. It only invites people to courses, and don't restricts the signup process to invited emails.

I'm working in the development of an auxilar plugin that restricts the signup process, but I'm not a programmer neither a developer, so I'd had a lot of problems in this process. There is someone who can help me in the development of the aux plugin? I'm working now with the SQL tables  who invitation plugin creates to save the emails and tokens generated