Option to approve new users

We host several spaces on our Confluence for different audiences. We have a space (A) for which we'd like to allow modifications by confluence-user. We'd like that space to be inviting. Now we want to add a space (B) for an undergraduate course but we don't want to invite undergrads to sign up for an account and mess around with (A). We give restrict (A) more but we'd rather not.

What would solve this dilemma for us is if each new account was inactive until the admin activated it. One way to do this would be that when a user signs up, the admin receives an e-mail with two links for Approve and Deny.

If you don't like this proposal, see the other one that's related.