AUTHENTICATION DEVICE, AUTHENTICATION METHOD, AND AUTHENTICATION PROGRAM WITH THE METHOD MOUNTED THEREON

For enabling single sign-on among applications, a linkage ID indicating connection between the authentication apparatus 1 including the client function and the server apparatus 2 is shared among a plurality of applications. For that, a SV information management unit Aa of the authentication apparatus 1 having the client function manages the linkage ID by storing it in a predetermined storing unit. An AP information management unit Ab manages and stores connection information between applications in a predetermined storing unit, wherein the connection information includes an application name corresponding to an application. Then, an AP decision unit determines whether an application name included in a received linkage ID request is registered in the AP information management unit Ab, obtains the linkage ID from the SV information management unit Aa when the application name is registered in the AP information management unit Ab, and returns the linkage ID to a source of the linkage ID request.