Internet Engineering Task Force K. Jaganathan Internet-Draft L. Zhu Document: draft-jaganathan-kerberos-http-00.txt J. Brezak Category: Informational Microsoft Corporation Expires: December 25, 2005 June 23, 2005 Kerberos based HTTP Authentication in Windows draft-jaganathan-kerberos-http-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 25, 2005. Copyright Notice Copyright (C) The Internet Society (2005). 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 are performed. This document explains how Jaganathan, et al. Expires December 25, 2005 [Page 1]
Internet-Draft HTTP Authentication in Windows June 2005 HTTP authentication utilizes the Simple and Protected GSS-API Negotiation mechanism. Details of SPNEGO implementation are not provided in this document. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . . . . 4 3. Access Authentication . . . . . . . . . . . . . . . . . . . . 5 3.1 Reliance on the HTTP/1.1 Specification . . . . . . . . . . 5 4. HTTP Negotiate Authentication Scheme . . . . . . . . . . . . . 6 4.1 The WWW-Authenticate Response Header . . . . . . . . . . . 6 4.2 The Authorization Request Header . . . . . . . . . . . . . 7 5. Negotiate Operation Example . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 7. Normative References . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 11 Intellectual Property and Copyright Statements . . . . . . . . 12 Jaganathan, et al. Expires December 25, 2005 [Page 2]
Internet-Draft HTTP Authentication in Windows June 2005 1. Introduction Microsoft has provided support for Kerberos authentication in MSIE and 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 and the Generic Security Services Application Program Interface(GSSAPI). Jaganathan, et al. Expires December 25, 2005 [Page 3]
Internet-Draft HTTP Authentication in Windows June 2005 2. Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Jaganathan, et al. Expires December 25, 2005 [Page 4]
Internet-Draft HTTP Authentication in Windows June 2005 3. Access Authentication 3.1 Reliance on the HTTP/1.1 Specification This specification is a companion to the HTTP/1.1 specification [RFC2616] and builds on the authentication mechanisms defined in [RFC2617]. It uses the augmented BNF section 2.1 of that document, and relies on both the non-terminals defined in that document and other aspects of the HTTP/1.1 specification. Jaganathan, et al. Expires December 25, 2005 [Page 5]
Internet-Draft HTTP Authentication in Windows June 2005 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 [RFC2078]. In particular, they follow the formats set for the SPNEGO [RFC2478] and Kerberos [RFC1964] mechanisms for GSSAPI. The "Negotiate" auth-scheme calls for the use of SPNEGO GSSAPI tokens which 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 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. 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 return a token for the client, this directive contains the base64 encoding of an InitialContextToken as defined in [RFC2078]. 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. For example the authentication could have failed on the final leg if mutual authentication was requested and the server was not able to Jaganathan, et al. Expires December 25, 2005 [Page 6]
Internet-Draft HTTP Authentication in Windows June 2005 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 [RFC1964] 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] utilized as follows: credentials = "Negotiate" auth-data2 auth-data2 = 1#( gssapi-data ) gssapi-data This directive contains is the base64 encoding of an InitialContextToken as defined in [RFC2078]. 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. Jaganathan, et al. Expires December 25, 2005 [Page 7]
Internet-Draft HTTP Authentication in Windows June 2005 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 and pass this into gss_init_security_context and return the new gssapi-data to the server. 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 WWW-Authenticate header with the final response containing the HTTP body. Jaganathan, et al. Expires December 25, 2005 [Page 8]
Internet-Draft HTTP Authentication in Windows June 2005 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. Jaganathan, et al. Expires December 25, 2005 [Page 9]
Internet-Draft HTTP Authentication in Windows June 2005 6. Security Considerations The SPNEGO HTTP authentication facility is only used to provide authentication of a user to 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 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. 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 with the security context is complete. At this point the data can be sent to the server. 7. Normative References [RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", RFC 1964, June 1996. [RFC2078] Linn, J., "Generic Security Service Application Program Interface, Version 2", RFC 2078, January 1997. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2478] Baize, E. and D. Pinkas, "The Simple and Protected GSS-API Negotiation Mechanism", RFC 2478, December 1998. [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Jaganathan, et al. Expires December 25, 2005 [Page 10]
Internet-Draft HTTP Authentication in Windows June 2005 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. Authors' 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.com Jaganathan, et al. Expires December 25, 2005 [Page 11]
Internet-Draft HTTP Authentication in Windows June 2005 Intellectual Property Statement 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 in BCP 78 and BCP 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 at http://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. Disclaimer of Validity 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. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Jaganathan, et al. Expires December 25, 2005 [Page 12]