Information processing system, information processing apparatus, and authentication method

An information processing system, which is implemented by one or more information processing apparatuses, includes a first receiving unit configured to receive a first user identifier and a first organization identifier via a network from an external apparatus and a first authentication unit configured to perform authentication based on the first user identifier and the first organization identifier by referring to a storage unit storing one or more second user identifiers in association with second organization identifiers. The first authentication unit performs authentication by identifying an organization identifier matching the first organization identifier within the second organization identifiers and identifying a user identifier matching the first user identifier within the second user identifiers associated with the matching organization identifier.