A device management system includes a frontend and a backend. The frontend includes a first domain. The backend includes a domain of a relay system as a relay backend domain that is a domain of the backend. The frontend accesses the relay backend domain when an access that uses a URL including the first domain as a domain name is received from a client via the relay system, and a request for an API is thus received from the client. The backend generates a relay Cookie including the relay backend domain as a domain used for establishing the session. The frontend transmits the relay Cookie to the client via the relay system.