What is an authentication server, and how does Active Directory satisfy this role?

What will be an ideal response?

An authentication server authenticates users or computers to the network so that they can access network resources. Active Directory, which is a directory service included in Windows Server, is often used for this purpose on a Windows domain. The authentication server stores user or device credentials, such as usernames and passwords, validates an authentication request, and determines the permissions assigned to each user, device, or group.