The Distributed Access Control System (DACS)is a light-weight single sign-on and attribute-based access control system for web servers and server-based software. DACS is primarily used with Apache web servers to provide enhanced access control for web pages, CGI programs and servlets, and other web-based assets, and to federateApache servers. In addition to simple web-based APIs, command-line interfaces are also provided to much of the functionality.Most web-based APIs can return XML or JSON documents. Development of DACS began in 2001, with the first open source release made available in 2005.