Roaming support

Hi all, I've a little problem with freeradius and I hope that someone could help me. I have 3 ap with coovachilli (configured to work with my freeradius 2.x server) connected to 3 xDSL. All work correct but when an user roam from an ap to another he have to reauhenticate itself (because the nas changed). I'm intrested to use UnLang to make freeradius able to check if user mac is already present in radacct table and if yes authorize user automatically. In this way every time an user roam from ap to another it colud be reauthentiated without asking for password. It is possible? Could anoyone help me in this? Rgds -- Filippo Sallemi