[Hampshire] Captive portal

Hi,

Does anyone know if there is an open source "captive portal"?

I am looking for a box that provides access control like you get in
airports or hotels.
I.e. User tries to get to a web site, but instead gets diverted to a
web page asking for credit card details etc, or a user login.
Only once the user has been identified, does it let them onto the
internet for real.

Kind Regards

James