Require social-connect to register

I would like to enable user registrations, but only if the user has a social-connect account (e.g., Facebook). There isn’t a setting that allows for this.

To get social-connect to work, I have to enable “Anyone can register”, but this also allows a new user to register without a social-connect account. I don’t want that.

I would like to request that social-connect add a setting that disables user registration without a social-connect account?

This behavior is desirable to reduce the spam accounts that get registered.