An Authentication Server is a system that verifies the identity of users or devices trying to access a network or application. It checks credentials, such as usernames and passwords, to ensure that only authorized individuals can gain access. This process helps protect sensitive information and resources from unauthorized users. These servers often work in conjunction with protocols like OAuth or LDAP to manage user permissions and roles. By centralizing authentication, organizations can streamline security measures and maintain better control over who can access their systems and data.