I'm trying to implement a signup flow in wordpress with the additional requirement that a user, to sign up, must use a secret activation code. Such code is valid only once, it's consumed after signup.
Many such codes are available (manually imported in DB is fine).
The use case is to let sign up only users who bought a (paper) book containing the secret activation code. In each book, the code will be different.
Before writing the whole thing manually, is there a plugin with a similar functionality? If not, what is the suggested implementation strategy?
There are a number of modules that already have this functionality, one that I've used before is simply "EasyInvitationCodes". There's also another one called "WP-Invites". If you use "invite" or "invitation" as your search keyword there are a few others available.
For EIC: https://wordpress.org/plugins/baw-invitation-codes/
For WP-Invites: https://wordpress.org/plugins/wp-invites/
Let me know if you've got any questions or if these aren't quite what you're after!