Authentication system, assistance server and non-transitory computer-readable recording medium encoded with assistance program

Authentication system includes an information processing apparatus, an authentication server and an assistance server, wherein the authentication server, in response to being requested to perform authentication of the user, performs authentication of the user using first authentication data that associates user identification information for identifying a registered user with first authentication information, and the assistance server, in response to detection of no registration of second authentication information that is different from the first authentication information of the user, acquires the first authentication data from the authentication server, and produces second authentication data that associates the second authentication information with the first authentication data.