I'm sure many companies/sites use it. It's the same as during signup when a site sends you an expiring confirmation link.
That can be easily achieved using a server side language like PHP and a database like MySQL. Thats the 'dynamic websites' idea.
And use cron jobs to delete expired access codes.
And other stuff and logic but basically, it can be easily done.
Last edited by Redcoder; 07-15-2012 at 10:46 AM..