An Internet service provider which provides network access via common modem or modem-like devices (be it PSTN, DSL, cable or GPRS/UMTS) can have one or more NAS (network access server) devices which accept PPP, PPPoE or PPTP connections, checking credentials and recording accounting data via back-end RADIUS servers, and allowing users access through that connection. The captive portal mechanism used by many WiFi providers: a user wants to access the Internet and opens a browser. The NAS detects that the user is not currently authorized to have access to the Internet, so the NAS prompts the user for their username and password.