<div class="content"><p>The <a href="ab2191b0-371a-497a-b184-eba073d04269#gt_bc2f6b5e-e5c0-408b-8f55-0350c24b9838" data-linktype="relative-path">SPNEGO</a>
Extended Negotiation Security Mechanism (NEGOEX) extends Simple and Protected
GSS-API Negotiation Mechanism (SPNEGO) described in <a href="https://go.microsoft.com/fwlink/?LinkId=90461" data-linktype="external">[RFC4178]</a>. SPNEGO
provides a negotiation mechanism for <a href="ab2191b0-371a-497a-b184-eba073d04269#gt_95f6b299-ec2f-4cef-87df-217f95bd9e14" data-linktype="relative-path">Generic Security Services (GSS)</a>
API (GSS-API), as described in <a href="https://go.microsoft.com/fwlink/?LinkId=90378" data-linktype="external">[RFC2743]</a>. NEGOEX is
based on the NEGOEX version 4 draft <a href="https://go.microsoft.com/fwlink/?linkid=2112888" data-linktype="external">[IETFDRAFT-NEGOEX-04]</a>
that enhances the capabilities of SPNEGO and provides a security mechanism that
can be negotiated by the SPNEGO protocol. NEGOEX defines a few new GSS-API
extensions that a security mechanism MUST support to be negotiated by NEGOEX.
This document defines these GSS-API extensions. Unlike SPNEGO, NEGOEX defines
its own way for signing the protocol messages to protect the protocol
negotiation.</p><p>The NEGOEX protocol is designed to address
the drawbacks of the SPNEGO negotiation model. When negotiated by SPNEGO,
NEGOEX uses the concepts developed in the GSS-API specification. The
negotiation data is encapsulated in context-level tokens. Therefore, callers of
the GSS-API do not need to be aware of the existence of the negotiation tokens
but only of the SPNEGO pseudo-security mechanism. When selected, NEGOEX
provides a method that allows selection of a common <a href="ab2191b0-371a-497a-b184-eba073d04269#gt_8e961bf0-95ba-4f58-9034-b67ccb27f317" data-linktype="relative-path">authentication</a> protocol. It
preserves the optimistic token semantics of SPNEGO and applies that
recursively. Accordingly, a context establishment mechanism token can be
included in the initial NEGOEX message, such that NEGOEX does not require an
extra round trip when the initiator’s or client’s optimistic token is accepted
by the target (or server acceptor).</p><p>Standard GSS has a strict interpretation of client (<a href="ab2191b0-371a-497a-b184-eba073d04269#gt_c66d2bda-f3e1-4d01-aa9e-8d790d3be5ab" data-linktype="relative-path">initiator</a>) and server (<a href="ab2191b0-371a-497a-b184-eba073d04269#gt_8dc36a3e-0f28-44b3-be31-c974593b62ad" data-linktype="relative-path">acceptor</a>). SPNEGO Extension
(SPNG) has extended [RFC4178] to allow the server to initiate SPNG message
flow. The message flow can begin from either the client or the server as the
initiator, whereas the receiver is the acceptor. See <a href="../ms-spng/f377a379-c24f-4a0f-a3eb-0d835389e28a" data-linktype="relative-path">[MS-SPNG]</a>
for client/server roles and variations.</p></div>