What type of authentication method is being used when a user is prompted for a username and password?

The authentication method in which a user is prompted for a username and password is classified as single-factor authentication. This approach relies on a single piece of evidence to verify the user's identity, which, in this case, is the combination of the username and password.

Single-factor authentication is commonly used because it is straightforward and easy to implement; users are required only to provide something they know (the username and password) to gain access to a system or application.

In contrast, multifactor authentication would require additional layers of security beyond just the username and password, such as a physical token or a biometric identifier, enhancing security by requiring two or more different authentication factors.

RADIUS and TACACS are protocols used for network authentication but do not themselves define the type of factor being utilized (single or multifactor). Their function is to facilitate the process of authentication across a network by providing centralized management, rather than describing the method itself. Thus, when only a username and password are required, it distinctly falls under the domain of single-factor authentication.