An authentication server that authenticates a user of a user terminal that plays a content stream provided by a content server, the authentication server authenticating the user. The authentication server includes storage means that stores registration information, authentication means that, when receiving an authentication request for content designated by a first user from a user terminal that the first user is using, compares information included in the authentication request with the registration information and authenticates the first user, generation means that, if the authentication succeeds, generates a first token indicating that the first user is an authenticated user, and communications means that transmits the generated first token to the user terminal. The generation means further generates a second token relating to the same content as the content designated by the first user, and the communications means is further configured to transmit the second token to the user terminal.