Routing Requests through an Authentication Service(client redirection model) INVITE 428 (w/Artifact-or Assertion)) INVITE (w/Artifact-or-Assertion) User Agent sip:alice@local.edu sip.remote.edu sip.local.edu User Agent INVITE sip:joe@remote.edu Joe (or even the Proxy Server) can inspect the Artifact/Assertion Auth Service attaches Artifact or Assertion to the SIP message |