\section{Third-Party Authentication}
\label{sec:thirdparty}

In some case, the RP actor may not be able to authenticate the requestor
or determine whether an authenticated user is authorized to make such a
request.  In these circumstances, the SIP entity may avail itself of
general SIP mechanisms that are not specific to this application.  The
authenticated identity management mechanism
\citenorm{draft-ietf-sip-identity} allows a third party to verify the
identity of the requestor and certify this towards an RP actor.  In
networks with mutual trust, the SIP asserted identity mechanism
\citeinform{rfc3325} can help the RP actor determine the identity of the
requestor.
