Expanded use of the Internet and technological advances are eliciting changes in how individuals manage and share their contents. The Internet has been primarily a client-server-based system, where it is challenging to keep contents up-to-date and consistent among all of the devices. Furthermore, the client-server model has service limitations in heterogeneous computing environments. However, a new peer-to-peer (P2P) model has emerged. In this P2P workplace, each participant (peer) acts as both client and content provider. Compared with services performed by the client-server model, P2P-based content management services have several advantages. In P2P environments, users can manage heterogeneous information resources residing in various platforms perhaps in different policy environments. A P2P-based content management model can provide higher resource availability due to the distributed nature of P2P computing. However, wide-scale application of P2P computing is constrained by limitations associated with the especially sophisticated control mechanisms needed between peers: most current P2P technologies simply focus on sharing services rather than on controls between the peers. In this paper, we introduce a middleware approach to support the underlying mechanisms, providing secure, automatic, interoperable, and transparent (SAINT) services for P2P content management. The underlying mechanisms are based on machine-understandable metadata. Our middleware approach using metadata facilitates the SAINT content management services with rich metadata expression in P2P computing environments. The broad dissemination of our approach allows the application of P2P technology to more reliable and efficient content services within organization or inter-organizations.