This recipe describes how to create a captive portal that will use a RADIUS server for authentication. RADIUS, which stands for Remote Authentication Dial-In User Service, is a network protocol that provides centralized Authentication, Authorization, and Accounting (AAA) management. It is implemented on a number of different platforms, including UNIX and Microsoft Windows servers. It is also often used by internet service providers (ISP) to provide access to the internet and email services. RADIUS operates on port 1812 and is an application-layer protocol. Although it was initially developed by a private company (Livingston Enterprises, Inc.), it now exists as an IETF standard. Authentication and authorization are described in RFC 2865, while accounting is described in RFC 2866.