Software for WLAN Hotspot

[Kay-Michael Voit <debian@voits.net>]

Hi,
I'm considering to build up a public wlan hotspot. I need time-limited 
authentification, mainly for identity logging purposes, not for billing.
I thougt about buying tickets (perhaps around 1 EUR/h) with time-limited 
username and password on it.

Where should I put in the authentification? At the proxy? Which software 
should I use? afaik I have to open the wlan, do I? How do commercial 
solutions work?

I need only very basic answer, only something to search for. I don't 
really know what to begin with....

Thanks in advance,
Kay