An alternative method to the smart card authentication is the two-factor authentication. This strong authentication type forces the user to connect to the assigned resources using the password and a second authentication key. In this recipe, we're going to discuss the configuration of the RADIUS (acronym of Remote Authentication Dial In User Service) authentication with the NetScaler Gateway, a strong authentication type based on the combination of a username, a password, and a pre-shared key, which can be delivered in the form of a static key or as a One Time Password (OTP).