A processing system including a first information processing system for managing user authentication information about a plurality of users belonging to at least one group and a second information processing system for acquiring information from the first information processing system and providing a service using the acquired information, the first information processing system comprises a first authentication means for receiving user authentication information from a user operating a client and for authenticating the user based on the received user authentication information; and a first transmission means for transmitting a set of group authentication information for the group to which the user belongs to the second information processing system in response to reception of a request for starting to use the service after the user is successfully authenticated, and the second information processing system comprises a second authentication means for receiving the transmitted set of group authentication information and for performing user authentication based on the received set of group authentication information; and a second transmission means for transmitting identification information, after the authentication has been successfully performed based on the set of group authentication information, indicating that the user authentication has been successfully performed to the first information processing system, wherein the first information processing system further comprising: an instruction means for transmitting the transmitted identification information to the client and for instructing the client to access the second information processing system, and a verification means, as part of the second information processing system, for verifying the identification information transmitted from the client performing access according to the instruction means; and a providing means for providing the service to the user operating the client without authenticating the user operating the client in response to the successful verification of the identification information. a first authentication means for receiving user authentication information from a user operating a client and for authenticating the user based on the received user authentication information; and a first transmission means for transmitting a set of group authentication information for the group to which the user belongs to the second information processing system in response to reception of a request for starting to use the service after the user is successfully authenticated, and a second authentication means for receiving the transmitted set of group authentication information and for performing user authentication based on the received set of group authentication information; and a second transmission means for transmitting identification information, after the authentication has been successfully performed based on the set of group authentication information, indicating that the user authentication has been successfully performed to the first information processing system, an instruction means for transmitting the transmitted identification information to the client and for instructing the client to access the second information processing system, and a verification means, as part of the second information processing system, for verifying the identification information transmitted from the client performing access according to the instruction means; and a providing means for providing the service to the user operating the client without authenticating the user operating the client in response to the successful verification of the identification information.