  Digital identity management intra and inter information systems, and, service
oriented architectures, are the roots of identity federation. This kind of
security architectures aims at enabling information system interoperability.
Existing architectures, however, do not consider interoperability of
heterogeneous federation architectures, which rely on different federation
protocols.In this paper, we try to initiate an in-depth reflection on this
issue, through the comparison of two main federation architecture
specifications: SAML and WS-Federation. We firstly propose an overall outline
of identity federation. We furthermore address the issue of interoperability
for federation architectures using a different federation protocol. Afterwards,
we compare SAML and WS-Federation. Eventually, we define the ways of
convergence, and therefore, of interoperability.
