An authentication system in which a authentication server and a plurality of clients are coupled through a network and configured to process an authentication from a user of a client, is configured to determine as a cache target user another user who is different from the user who requested the authentication; is configured to generate an identifier that indicates the cache target user; and is configured to transmit biometric data of the cache target user and the identifier to the client from which the authentication of the user was requested. A cache availability determiner can determine whether biometric data of any cache target user are available on a client.