A management system, a communication system, and a management method. The management system and the management method include receiving a request to associate identification information of a first user with identification information of a first client application that the first user is authorized to use, and identification information of a second user who has been authenticated and has been authorized to use a second client application, determining whether the identification information of the second user matches certain information that corresponds to the first client application, and associating the identification information of the first user with the identification information of the first client application when the determining determines that the identification information of the second user matches the certain information that corresponds to the first client application. The communication system includes the management system, and a communication terminal that sends the access token to the management system.