DS-1028 Implementation of CAS (Single Sign-On) authentication for DSpace

CAS Authentication with optional SAML attribute values dicovery for DSpace 4_x and hopefully 5.0.

The first patch was formerly implemented by Kaboré Wendin-Malegdé Patrick at JIRA (https://jira.duraspace.org/browse/DS-1028) and further user kgunn at JIRA did some arrangements to make it work with DSpace 1.8.2 and CAS 3.1.x. Finally nkneumann updated it to work with DSpace 3.1 (https://github.com/nkneumann/DSpace/commit/53e02e14ae0994ebdfccc8dc4842cada6ef08573).

This patch extends the work done by nkneumann by fixing it for DSpace 4_x and allowing usage of SAML to get user attributes.