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Network Working Group                                      K. JaganathanRequest for Comments: 4559                                        L. ZhuCategory: Informational                                        J. Brezak                                                   Microsoft Corporation                                                               June 2006SPNEGO-based Kerberos and NTLM HTTP Authenticationin Microsoft WindowsStatus of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2006).Abstract   This document describes how the Microsoft Internet Explorer (MSIE)   and Internet Information Services (IIS) incorporated in Microsoft   Windows 2000 use Kerberos for security enhancements of web   transactions.  The Hypertext Transport Protocol (HTTP) auth-scheme of   "negotiate" is defined here; when the negotiation results in the   selection of Kerberos, the security services of authentication and,   optionally, impersonation (the IIS server assumes the windows   identity of the principal that has been authenticated) are performed.   This document explains how HTTP authentication utilizes the Simple   and Protected GSS-API Negotiation mechanism.  Details of Simple And   Protected Negotiate (SPNEGO) implementation are not provided in this   document.Table of Contents1. Introduction ....................................................22. Conventions Used in This Document ...............................23. Access Authentication ...........................................23.1. Reliance on the HTTP/1.1 Specification .....................24. HTTP Negotiate Authentication Scheme ............................24.1. The WWW-Authenticate Response Header .......................25. Negotiate Operation Example .....................................46. Security Considerations .........................................57. Normative References ............................................6Jaganathan, et al.           Informational                      [Page 1]

RFC 4559        HTTP Authentication in Microsoft Windows       June 20061.  Introduction   Microsoft has provided support for Kerberos authentication in   Microsoft Internet Explorer (MSIE) and Internet Information Services   (IIS), in addition to other mechanisms.  This provides the benefits   of the Kerberos v5 protocol for Web applications.   Support for Kerberos authentication is based on other previously   defined mechanisms, such as SPNEGO Simple And Protected Negotiate   (SPNEGO) [RFC4178] and the Generic Security Services Application   Program Interface(GSSAPI).2.  Conventions Used in This Document   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to   be interpreted as described in [RFC2119].3.  Access Authentication3.1.  Reliance on the HTTP/1.1 Specification   This specification is a companion to the HTTP/1.1 specification   [RFC2616], and it builds on the authentication mechanisms defined in   [RFC2617].  It uses the augmented BNF section of that document (2.1),   and it relies on both the non-terminals defined in that document and   other aspects of the HTTP/1.1 specification.4.  HTTP Negotiate Authentication Scheme   Use of Kerberos is wrapped in an HTTP auth-scheme of "Negotiate".   The auth-params exchanged use data formats defined for use with the   GSS-API [RFC2743].  In particular, they follow the formats set for   the SPNEGO [RFC4178] and Kerberos [RFC4121] mechanisms for GSSAPI.   The "Negotiate" auth-scheme calls for the use of SPNEGO GSSAPI tokens   that the specific mechanism type specifies.   The current implementation of this protocol is limited to the use of   SPNEGO with the Kerberos and Microsoft(NT Lan Manager) NTLM   protocols.4.1.  The WWW-Authenticate Response Header   If the server receives a request for an access-protected object, and   if an acceptable Authorization header has not been sent, the server   responds with a "401 Unauthorized" status code, and a "WWW-   Authenticate:" header as per the framework described in [RFC2616].   The initial WWW-Authenticate header will not carry any gssapi-data.Jaganathan, et al.           Informational                      [Page 2]

RFC 4559        HTTP Authentication in Microsoft Windows       June 2006   The negotiate scheme will operate as follows:           challenge       = "Negotiate" auth-data           auth-data       = 1#( [gssapi-data] )   The meanings of the values of the directives used above are as   follows:   gssapi-data   If the gss_accept_security_context returns a token for the client,   this directive contains the base64 encoding of an   initialContextToken, as defined in [RFC2743].  This is not present in   the initial response from the server.   A status code 200 status response can also carry a "WWW-Authenticate"   response header containing the final leg of an authentication.  In   this case, the gssapi-data will be present.  Before using the   contents of the response, the gssapi-data should be processed by   gss_init_security_context to determine the state of the security   context.  If this function indicates success, the response can be   used by the application.  Otherwise, an appropriate action, based on   the authentication status, should be taken.   For example, the authentication could have failed on the final leg if   mutual authentication was requested and the server was not able to   prove its identity.  In this case, the returned results are suspect.   It is not always possible to mutually authenticate the server before   the HTTP operation.  POST methods are in this category.   When the Kerberos Version 5 GSSAPI mechanism [RFC4121] is being used,   the HTTP server will be using a principal name of the form of   "HTTP/hostname".4.2.  The Authorization Request Header   Upon receipt of the response containing a "WWW-Authenticate" header   from the server, the client is expected to retry the HTTP request,   passing a HTTP "Authorization" header line.  This is defined   according to the framework described in [RFC2616] and is utilized as   follows:           credentials             = "Negotiate" auth-data2           auth-data2              = 1#( gssapi-data )   gssapi-dataJaganathan, et al.           Informational                      [Page 3]

RFC 4559        HTTP Authentication in Microsoft Windows       June 2006   This directive contains the base64 encoding of an   InitialContextToken, as defined in [RFC2743].   Any returned code other than a success 2xx code represents an   authentication error.  If a 401 containing a "WWW-Authenticate"   header with "Negotiate" and gssapi-data is returned from the server,   it is a continuation of the authentication request.   A client may initiate a connection to the server with an   "Authorization" header containing the initial token for the server.   This form will bypass the initial 401 error from the server when the   client knows that the server will accept the Negotiate HTTP   authentication type.5.  Negotiate Operation Example   The client requests an access-protected document from server via a   GET method request.  The URI of the document is   "http://www.nowhere.org/dir/index.html".           C: GET dir/index.html   The first time the client requests the document, no Authorization   header is sent, so the server responds with           S: HTTP/1.1 401 Unauthorized           S: WWW-Authenticate: Negotiate   The client will obtain the user credentials using the SPNEGO GSSAPI   mechanism type to identify generate a GSSAPI message to be sent to   the server with a new request, including the following Authorization   header:           C: GET dir/index.html           C: Authorization: Negotiate a87421000492aa874209af8bc028   The server will decode the gssapi-data and pass this to the SPNEGO   GSSAPI mechanism in the gss_accept_security_context function.  If the   context is not complete, the server will respond with a 401 status   code with a WWW-Authenticate header containing the gssapi-data.           S: HTTP/1.1 401 Unauthorized           S: WWW-Authenticate: Negotiate 749efa7b23409c20b92356   The client will decode the gssapi-data, pass this into   Gss_Init_security_context, and return the new gssapi-data to the   server.Jaganathan, et al.           Informational                      [Page 4]

RFC 4559        HTTP Authentication in Microsoft Windows       June 2006           C: GET dir/index.html           C: Authorization: Negotiate 89a8742aa8729a8b028   This cycle can continue until the security context is complete.  When   the return value from the gss_accept_security_context function   indicates that the security context is complete, it may supply final   authentication data to be returned to the client.  If the server has   more gssapi data to send to the client to complete the context, it is   to be carried in a WWW-Authenticate header with the final response   containing the HTTP body.           S: HTTP/1.1 200 Success           S: WWW-Authenticate: Negotiate ade0234568a4209af8bc0280289eca   The client will decode the gssapi-data and supply it to   gss_init_security_context using the context for this server.  If the   status is successful from the final gss_init_security_context, the   response can be used by the application.6.  Security Considerations   The SPNEGO HTTP authentication facility is only used to provide   authentication of a user to a server.  It provides no facilities for   protecting the HTTP headers or data including the Authorization and   WWW-Authenticate headers that are used to implement this mechanism.   Alternate mechanisms such as TLS can be used to provide   confidentiality.  Hashes of the TLS certificates can be used as   channel bindings to secure the channel.  In this case clients would   need to enforce that the channel binding information is valid.  Note   that Kerb-TLS [RFC2712] could be used to provide both authentication   and confidentiality, but this requires a change to the TLS provider.   This mechanism is not used for HTTP authentication to HTTP proxies.   If an HTTP proxy is used between the client and server, it must take   care to not share authenticated connections between different   authenticated clients to the same server.  If this is not honored,   then the server can easily lose track of security context   associations.  A proxy that correctly honors client to server   authentication integrity will supply the "Proxy-support:  Session-   Based-Authentication" HTTP header to the client in HTTP responses   from the proxy.  The client MUST NOT utilize the SPNEGO HTTP   authentication mechanism through a proxy unless the proxy supplies   this header with the "401 Unauthorized" response from the server.Jaganathan, et al.           Informational                      [Page 5]

RFC 4559        HTTP Authentication in Microsoft Windows       June 2006   When using the SPNEGO HTTP authentication facility with client-   supplied data such as PUT and POST, the authentication should be   complete between the client and server before sending the user data.   The return status from the gss_init_security_context will indicate   that the security context is complete.  At this point, the data can   be sent to the server.7.  Normative References   [RFC2743]  Linn, J., "Generic Security Service Application Program              Interface Version 2", 2, Update 1", 2743, January 2000.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC4178] Zhu, L., Leach, P., Jaganathan, K., and W. Ingersoll, "The              Simple and Protected GSS-API Generic Security Service              Application Program Interface (GSS-API) Negotiation              Mechanism", 4178, October 2005.   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext              Transfer Protocol -- HTTP/1.1",RFC 2616, June 1999.   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,              Leach, P., Luotonen, A., and L. Stewart, "HTTP              Authentication: Basic and Digest Access Authentication",RFC 2617, June 1999.   [RFC2712]  Medvinsky, A. and M. Hur, "Addition of Kerberos Cipher              Suites to Transport Layer Security (TLS)",RFC 2712,              October 1999.   [RFC4121]  Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos              Version 5 Generic Security Service Application Program              Interface (GSS-API) Mechanism: Version 2",RFC 4121, July              2005.Jaganathan, et al.           Informational                      [Page 6]

RFC 4559        HTTP Authentication in Microsoft Windows       June 2006Authors' Addresses   Karthik Jaganathan   Microsoft Corporation   One Microsoft Way   Redmond, WA  98052   US   EMail: karthikj@microsoft.com   Larry Zhu   Microsoft Corporation   One Microsoft Way   Redmond, WA  98052   US   EMail: lzhu@microsoft.com   John Brezak   Microsoft Corporation   One Microsoft Way   Redmond, WA  98052   US   EMail: jbrezak@microsoft.comJaganathan, et al.           Informational                      [Page 7]

RFC 4559        HTTP Authentication in Microsoft Windows       June 2006Full Copyright Statement   Copyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78 and at www.rfc-editor.org/copyright.html, and   except as set forth therein, the authors retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is provided by the IETF   Administrative Support Activity (IASA).Jaganathan, et al.           Informational                      [Page 8]