Authenticate user using CAS.

Authfront.cas is based on phpCAS library of JASIG that turns Pydio to be able be integrated into a SSO system. It can do the authentication on a remote server CAS by using two mode: client and proxy * In mode client, authfront.cas runs as a cas client to authenticate given user's credential to remote server CAS. * In mode proxy, it can provide additionally authentication service to another service such as smb/cifs or imap ... Note: The connection between pydio and cas normally is an ssl connection. Administrator must take attention on configuration of certificate and trusted relationship of two direction between Pydio server and CAS.