Add detailed federation configuration docs

[OpenStack Infra]

https://review.openstack.org/89220
commit 50cccf94fd12aa0fc8205d018c306bc493d89575
Author: Marek Denis <email address hidden>
Date: Thu Apr 17 00:50:09 2014 -0500

    Add detailed federation configuration docs

    Add documentation on how to configure federation in keystone

    Co-Authored-By: Steve Martinelli <email address hidden>

    DocImpact
    Closes-Bug: #1311693
    Change-Id: Ia7e5a67d762921a81ef4a7d16c682e5db1c3ba6c

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/118237

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/118237
Committed: https://git.openstack.org/cgit/openstack/security-doc/commit/?id=244daa86fee69e79b86e65e4ce57a16d8cdcb168
Submitter: Jenkins
Branch: master

commit 244daa86fee69e79b86e65e4ce57a16d8cdcb168
Author: Deepti Navale <email address hidden>
Date: Tue Aug 26 14:29:06 2014 +1000

    Included info about Federated Identity

    Updated the Security guide to include information about the overview of
    Federated identity, the terms used and how Identity Service handles mapping of SAML
    assertions to assigned roles.
    Also included some steps for configuring Identity Service for federation.
    Partial-Bug: #1319158

    Change-Id: I0d0307f26935d4e5d09ea00d0f95f7e41dbfdb50