Login with only a registration-number

Hi, as asked on http://drupal.org/node/142607#comment-1719940 a new issue build.

I have a usecase in which I want users to take survey anonymous, but only allow people to take the survey if they have gotten a registration number in another email.
It would be great if with this module the user should be able to login only with a registration-number and then per registration-number should only be able to take the related survey.

Thanks for considering this!
Greetings, Martijn