Password protect registration form

Hi everybody,
for a customer I need to build a CB-based site, where registration must only be possible for certain users. My customers wants the folloing procedure:
Users, who want access to the site, must contact my customer in order to be confirmed. When the user is confirmed he gets a password to unlock the websites' registration form, so he can register with the site. How can this be done?
I have tried this by creating a specific user and redirecting him to the registration form using cb_autoactions but I couldn't figure out the right trigger. Also: is there a more elegant way to do this?

Easiest approach is to install CB Invites and set its invite code field to display on registration and be required. You'd then just need to send an invite (will send via email) to the user where they can supply the invite code during registration to allow them to registered (it'll pre-fill the invite code field if they click the invite URL).

Alternative is you could create a database table to store the access codes you're generating for customers. Next add a text field to the registration field where they'll supply that access code. Now you'll need to install CB Query Field and setup Query Validation for that text field to validate against your access code database table.

Hello Krileon,
thank you for these tips. I'll try them and get back if I have problems.
Best Regards