An information processing system which provides Web services and is capable of communicating with a client and at least one authentication device for providing an authentication service for requesting entry of authentication information and performing authentication processing, the information processing system comprising: providing means configured to provide the Web services conditional upon authentication processing performed by the authentication device without requesting entry of authentication information necessary for the authentication processing in an information processing apparatus; storage means configured to store key information for determining an authentication device and address information of the authentication device associated with said key information; and access instruction means configured to, in a case where an access request from the client is an unauthenticated access request that has not received the authentication processing service, specify the key information which coincides with key information acquired as a result of the access request and is stored by the storage means, transmit to the client the address information of the authentication device stored by being associated with the specified key information, and issue a redirect instruction to the client such that the client accesses said authentication device in order to receive the authentication processing service; wherein said authentication device is one of an authentication device that exists in the same security domain as a device having the providing means and an authentication device that does not exist in the same security domain as a device having the providing means; and wherein, when the authentication device accessed by the client based on the redirect instruction does not exist in the same security domain as a device having the providing means, the providing means is configured to provide the Web services upon verification, by an authentication device that exists in the same security domain as a device having the providing means, of an assertion generated by the authentication device that does not exist in the same security domain as a device having the providing means. providing means configured to provide the Web services conditional upon authentication processing performed by the authentication device without requesting entry of authentication information necessary for the authentication processing in an information processing apparatus; storage means configured to store key information for determining an authentication device and address information of the authentication device associated with said key information; and access instruction means configured to, in a case where an access request from the client is an unauthenticated access request that has not received the authentication processing service, specify the key information which coincides with key information acquired as a result of the access request and is stored by the storage means, transmit to the client the address information of the authentication device stored by being associated with the specified key information, and issue a redirect instruction to the client such that the client accesses said authentication device in order to receive the authentication processing service; wherein said authentication device is one of an authentication device that exists in the same security domain as a device having the providing means and an authentication device that does not exist in the same security domain as a device having the providing means; and wherein, when the authentication device accessed by the client based on the redirect instruction does not exist in the same security domain as a device having the providing means, the providing means is configured to provide the Web services upon verification, by an authentication device that exists in the same security domain as a device having the providing means, of an assertion generated by the authentication device that does not exist in the same security domain as a device having the providing means.