An authentication system, a communication system, and an authentication method. The authentication system and the authentication method include receiving additional information where first identification information of a communication terminal is added to second identification information of a target to be authenticated, and authenticating the target to be authenticated using the second identification information of the target to be authenticated. When the target to be authenticated is authenticated by the authenticating, an account associated with the additional information is authorized to receive information that is sent from the communication terminal to another communication terminal. The communication system includes the authentication system and an authorization system including circuitry to authorize the account associated with the authorization data to receive information that is sent from the communication terminal to another communication terminal when the target to be authenticated is authenticated by the first circuitry.