Require invitation code for registration

We'd like to set up our Wiki such that registration by new users is only possible if they are able to provide an invitation code. We don't require per-user invitation codes, a single invitation code for any new registration would suffice.

Are there any plugins available that implement this sort of behavior?

Thanks,
Stephan

---

I'm not aware of any extension for this feature. One simple solution might be to require HTTP user authentication to access the register script, and provide a simple user/password to pass to people you want to register for your site.

<Directory "/var/www/foswiki/trunk/core/bin">
...  (other settings not changed)

    <FilesMatch "^(register.*)$">
        SetHandler cgi-script
        AuthUserFile /var/www/foswiki/trunk/core/data/regpass
        AuthName 'Enter username invite - Password per your invitation'
        AuthType Basic
       Require invite
       Satisfy All
    </FilesMatch>
...
</Directory>

Create the alternate password file:

~ $ htpasswd -cs regpass invite       
New password: 
Re-type new password: 
Adding password for user invite