Allow users to register as a higher role than default with code

Question

By default all new registrants for my site are assigned the role "contributor" and then I make them request an upgrade to an "author" account through a form. I also send out invitations to certain people to join the site in which I want them to automatically register as an "author" so they can skip the application process.

Now my first thought was to send out some type of key code in the email and have them enter it in on a registration page but that seems like a lot of hassle. What I'd like to do instead is send them a link to a registration page that signs them up under the "author" role. But I also have issues with that approach in that I would need the link to only work when accessed by that email address it was sent too.

I know this is a vague question but I'm looking for a solid solution for what I want to do.

Answer 1

You could combine your two ideas- generate a code and send them a link to a sign up form with that code as a query string in the url. match the code with the email address they enter when they sign up, then delete it once sign up is complete so it can't be used again.