The Distributed Access Control System (DACS) is a light-weight single sign-on androle-based access control system forweb serversandserver-based software.DACS is primarily used withApache web serversto provide enhanced access controlfor web pages,CGI programsand servlets,and other web-based assets,and to federateApache servers.Released under an open source license, DACS provides a modular authenticationframeworkthat supports an array of common authentication methods and a rule-based authorization enginethat can grant or deny access to resources,named by URLs,based on the identity of the requestor and other contextual information.Administrators can configure DACS to identify users by employing authentication methods and user accountsalready available within their organization.The resulting DACS identities are recognized at all DACS jurisdictions that have been federated.In addition to simple web-basedAPIs,command-line interfaces are also provided to much of the functionality.Development of DACS began in 2001,with the first open source release made available in 2005.