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Presence services are not widespread because there is little interest in a closed presence application in the IP multimedia subsystem/next-generation network (IMS/NGN). A representational state transfer (REST) API for a presence service in IMS/NGN that can be easily used in a Web application has been proposed to encourage the use of presence services in IMS/NGN. Two problems with the conventional method for a presence REST API are presence authorization in Web applications and increased SIP processing within the IMS. This paper describes these problems in detail, proposes functions and analysis for solving them, and presents a prototype application.