The Certificate System employs Red Hat Fortitude as its HTTP engine; this runs secure Tomcat for the CA, OCSP, TKS, and DRM subsystems and secure Apache for TPS. Fortitude supports the subsystem instance HTTP interfaces and provides the entry point for all users and applications to access Certificate System subsystem functions through the different user interfaces: administrative console, agent services, and end-entities pages. The subsystem pages are accessed over HTTP, but they are created by subsystem-specific servlets contained in the Certificate System. While the HTTP engine provides the connection entry points, Certificate System completes the interfaces by providing the servlets specific to each interface. These servlets can return data in HTML or XML formats, making it easier for system administrators to write scripts which interact with these servlets. For more information, see Section 4.8, “Using Java Servlets”.