  Clarens is a uniquely flexible web services infrastructure providing a
unified access protocol to a diverse set of functions useful to the HEP
community. It uses the standard HTTP protocol combined with application layer,
certificate based authentication to provide single sign-on to individuals,
organizations and hosts, with fine-grained access control to services, files
and virtual organization (VO) management. This contribution describes the
server functionality, while client applications are described in a subsequent
talk.
