Magic Link but for Registration?

[EliMariaaaa]

This is just a what-if question. Is it possible to use magic link but for Registration? The reason is, that I have a requirement where if the user hasn't submitted an entry to a specific form, the web app would not allow that user to register. I know it can be achieved by checking in the DB if he/she already submitted, but I want the admin to have the discretion and just give a magic link to a user he/she wants to register without doing the checking. The register link is easy to guess and can be easily shared with others since it's a fixed link.

So I don't want them to simply access the /register URL but through that magic link.