SPNEGO

Simple and Protected GSSAPI Negotiation Mechanism (SPNEGO), often pronounced "spenay-go", is a GSSAPI "pseudo mechanism" used by client-server software to negotiate the choice of security technology. SPNEGO is used when a client application wants to authenticate to a remote server, but neither end is sure what authentication protocols the other supports. The pseudo-mechanism uses a protocol to determine what common GSSAPI mechanisms are available, selects one and then dispatches all further security operations to it. This can help organizations deploy new security mechanisms in a phased manner.

SPNEGO's most visible use is in Microsoft's "HTTP Negotiate" authentication extension. It was first implemented in Internet Explorer 5.01 and IIS 5.0 and provided single sign-on capability later marketed as Integrated Windows Authentication. The negotiable sub-mechanisms included NTLM and Kerberos, both used in Active Directory. The HTTP Negotiate extension was later implemented with similar support in:

• Mozilla 1.7 beta^[1]
• Mozilla Firefox 0.9
• Konqueror 3.3.1^[2]
• Google Chrome 6.0.472^[3]

• 19 February 1996 – Eric Baize and Denis Pinkas publish the Internet Draft Simple GSS-API Negotiation Mechanism (draft-ietf-cat-snego-01.txt).
• 17 October 1996 – The mechanism is assigned the object identifier 1.3.6.1.5.5.2 and is abbreviated snego.
• 25 March 1997 – Optimistic piggybacking of one mechanism's initial token is added. This saves a round trip.
• 22 April 1997 – The "preferred" mechanism concept is introduced. The draft standard's name is changed from just "Simple" to "Simple and Protected" (spnego).
• 16 May 1997 – Context flags are added (delegation, mutual auth, etc.). Defenses are provided against attacks on the new "preferred" mechanism.
• 22 July 1997 – More context flags are added (integrity and confidentiality).
• 18 November 1998 – The rules of selecting the common mechanism are relaxed. Mechanism preference is integrated into the mechanism list.
• 4 March 1998 – An optimisation is made for an odd number of exchanges. The mechanism list itself is made optional.
• December 1998 (Final) – DER encoding is chosen to disambiguate how the MIC is calculated. The draft is submitted for standardisation as RFC 2478.
• October 2005 – Interoperability with Microsoft implementations is addressed. Some constraints are improved and clarified and defects corrected. Published as RFC 4178, although it is now non-interoperable with strict implementations of now-obsoleted RFC 2478.

• "Internet Drafts of RFC 4178". All (Current & Expired) Internet Drafts Collection – Drafts. Retrieved 23 August 2014.
• "HTTP-Based Cross-Platform Authentication via the Negotiate Protocol". Microsoft Developer Network (MSDN) library. Retrieved 8 October 2015.
• "using mod_auth_kerb and Windows 2000/2003 as KDC". Tutorial. Retrieved 2 December 2005.

• RFC 4178 The Simple and Protected GSS-API Negotiation Mechanism (obsoletes RFC 2478).
• RFC 4559 SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows