Kerberos working group J.Brezak Internet Draft Microsoft Document: draft-brezak-spnego-http-01.txt Category: Informational September 2001 HTTP Authentication: SPNEGO Access Authentication Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. 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. 1. Abstract This document describes how Microsoft's Internet Explorer 5.0 and Internet Information Services 5.0 use Kerberos for security enhancements of web transactions. The 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. 2. Conventions used in this document In examples, "C:" and "S:" indicate lines sent by the client and server respectively. 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 RFC-2119 [3]. 3. Access Authentication 3.1 Reliance on the HTTP/1.1 Specification This specification is a companion to the HTTP/1.1 specification [4] and builds on the authentication mechanisms defined in [5]. It uses Brezak Category - Informational 1 SPNEGO Access Authentication September 2001 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. 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 [6]. In particular, they follow the formats set for the SPNEGO [7] and Kerberos [8] "mechanisms" for GSSAPI. The "Negotiate" auth-scheme calls for the use of SPNEGO GSSAPI tokens which the specific mechanism type specifies. 4.1 The WWW-Authenticate Response Header If the server receives a request for an access-protected object, and an acceptable Authorization header is not sent, the server responds with a "401 Unauthorized" status code, and a WWW-Authenticate header as per the framework described in [4]. 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 is the base64 encoding of an InitialContextToken as defined in [6]. A status code 200 response can also carry a WWW-Authenticate response header containing the final leg of a authentication. 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 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 [RFC-1964] is being used, the HTTP server will be using a principal name of the form of "http/<hostname>". 4.2 The Authorization Request Header Brezak Category - Informational 2 SPNEGO Access Authentication September 2001 The client is expected to retry the request, passing an Authorization header line, which is defined according to the framework described in [4] utilized as follow: credentials = "Negotiate" auth-data2 auth-data2 = 1#( gssapi-data ) gssapi-data This directive contains is the base64 encoding of an InitialContextToken as defined in [6]. If a directive or its value is improper, or required directives are missing, the propose response is 400 Bad Request. If a 401 Unauthorized status code is returned, the contents of the WWW- Authenticate response header is used to continue the authentication as long as the opaque value is the same. 5. Negotiate Operation Example The user is logged onto realm A.COM as user@A.COM. The web server is in realm B using the principal http/server@B.COM. Realm B.COM trusts Realm A.COM 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". The first time the client requests the document, no Authorization header is sent, so the server responds with: HTTP/1.1 401 Unauthorized 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: Authorization: Negotiate 2a87421000492ade0234568ac0289eca874209af8bc028 The server will decode the gssapi-data and pass this to the SPNEGO GSSAPI mechanism in the gss_accept_security_context function. The return value from the gss_accept_security_context function can indicate the security context is complete and 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. The response will be sent to the client, including the following header: HTTP/1.1 200 Success WWW-Authenticate: Negotiate ade0234568ac874209af8bc0280289eca Brezak Category - Informational