RADIUS

Remote Authentication Dial-in User Service (RADIUS): A protocol that provides AAA services for users on a network

• a very common protocol used to manage access to internal networks, ​WiFi networks, email services and VPN services

Clients who want ​to authenticate to a RADIUS server don’t directly interact with it. ​Instead, when a client wants to access a resource that’s protected, ​the client will present authentication credentials to a NAS, ​or network access server, which will relay the credentials to the RADIUS server.  ​The RADIUS server will then verify the credentials using a configured ​authentication scheme.