OpenSSO Enterprise provides both Java API and C API for writing clients that remote applications can use to administer policies and evaluate policy decisions. They are used to add, lookup, modify or replace policies, and to evaluate policy decisions when a principal attempts an action on a protected resource. Communication between the API and the Policy Service occurs by sending XML messages over HTTP(S). Additionally, you can extend and customize the Policy Service using the SPI. The classes are used by service developers and policy administrators who need to provide additional policy features as well as support for legacy policies. For example, you can develop customized plug-ins for creating custom policy subjects, referrals, conditions, and response providers. Lastly, the Client SDK is provided to implement policy evaluation logic on a remote web server or application server. For information, see Chapter 14, Using the Client SDK, in Sun OpenSSO Enterprise 8.0 Developer’s Guide, Chapter 2, Using the Policy Service API, in Sun OpenSSO Enterprise 8.0 Developer’s Guide, the Sun OpenSSO Enterprise 8.0 C API Reference for Application and Web Policy Agent Developers, and the Sun OpenSSO Enterprise 8.0 Java API Reference.