In a multi-domain environment, an access control apparatus belonging to a first domain obtains access control information for controlling usage of a function of an image forming apparatus corresponding to a user belonging to the first domain. When the user belonging to the first domain instructs usage of a function of an image forming apparatus belonging to a second domain, the access control apparatus belonging to the first domain requests an access control apparatus belonging to the second domain to add authentication information managed by the second domain to the access control information. The access control apparatus belonging to the first domain transmits access control information including the added authentication information to a client computer.