| blob | 0b8dcd73010c3df7e60a3fb66603e0c44ec04247 |
2 J.Brezak
3 Internet Draft Microsoft
4 Document: draft-brezak-kerberos-http-00.txt
5 Category: Informational November 17,2003
6 Expires: May 17,2003
9 HTTP Authentication: Kerberos Authentication
10 As implemented in Microsoft Windows 2000
13 Status of this Memo
15 This document is an Internet-Draft and is subject to all provisions
16 of Section 10 of RFC2026 [1] except that the right to create
17 derivative works is not granted. Internet-Drafts are working
18 documents of the Internet Engineering Task Force (IETF), its areas,
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20 working documents as Internet-Drafts. Internet-Drafts are draft
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23 inappropriate to use Internet- Drafts as reference material or to
24 cite them other than as "work in progress."
26 The list of current Internet-Drafts can be accessed at
27 http://www.ietf.org/ietf/1id-abstracts.txt
29 The list of Internet-Draft Shadow Directories can be accessed at
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32 1. Abstract
34 This document describes how the Microsoft Internet Explorer (MSIE)
35 and Internet Information Services (IIS) incorporated in Microsoft
36 Windows 2000 use Kerberos for security enhancements of web
37 transactions. The Hypertext Transport Protocol (HTTP) auth-scheme of
38 "negotiate" is defined here; when the negotiation results in the
39 selection of Kerberos, the security services of authentication and
40 optionally impersonation are performed.
42 This document explains how HTTP authentication utilizes the Simple
43 and Protected GSS-API Negotiation mechanism. Details of SPNEGO
44 implementation are not provided in this document.
47 2. Conventions used in this document
49 In examples, "C:" and "S:" indicate lines sent by the client and
50 server respectively.
52 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
53 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
54 this document are to be interpreted as described in RFC-2119 [1].
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58 HTTP Kerberos Access Authentication November 2003
60 3. Introduction
61 Microsoft has provided support for Kerberos authentication in MSIE
62 and IIS in addition to other mechanisms. This provides the benefits
63 of the Kerberos v5 protocol for Web applications.
64 Support for Kerberos authentication is based on other previously
65 defined mechanisms such as SPNEGO and the Generic Security Services
66 Application Program Interface(GSSAPI).
68 3. Access Authentication
70 3.1 Reliance on the HTTP/1.1 Specification
72 This specification is a companion to the HTTP/1.1 specification [1]
73 and builds on the authentication mechanisms defined in [2]. It uses
74 the augmented BNF section 2.1 of that document, and relies on both
75 the non-terminals defined in that document and other aspects of the
76 HTTP/1.1 specification.
79 4. HTTP Negotiate Authentication Scheme
81 Use of Kerberos is wrapped in an HTTP auth-scheme of "Negotiate".
82 The auth-params exchanged use data formats defined for use with the
83 GSS-API [3]. In particular, they follow the formats set for the
84 SPNEGO [4] and Kerberos [5] mechanisms for GSSAPI. The "Negotiate"
85 auth-scheme calls for the use of SPNEGO GSSAPI tokens which the
86 specific mechanism type specifies.
88 The current implementation of this protocol is limited to the use of
89 SPNEGO with the Kerberos and Microsoft(NT Lan Manager) NTLM
90 protocols.
92 4.1 The WWW-Authenticate Response Header
94 If the server receives a request for an access-protected object, and
95 an acceptable Authorization header has not been sent, the server
96 responds with a "401 Unauthorized" status code, and a "WWW-
97 Authenticate:" header as per the framework described in [1]. The
98 initial WWW-Authenticate header will not carry any gssapi-data.
100 The negotiate scheme will operate as follows:
102 challenge = "Negotiate" auth-data
103 auth-data = 1#( [gssapi-data] )
105 The meanings of the values of the directives used above are as
106 follows:
108 gssapi-data
109 If the gss_accept_security_context return a token for the
110 client, this directive contains the base64 encoding of an
111 InitialContextToken as defined in [3]. This is not present in
112 the initial response from the server.
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116 HTTP Kerberos Access Authentication November 2003
118 A status code 200 status response can also carry a "WWW-
119 Authenticate" response header containing the final leg of an
120 authentication. In this case, the gssapi-data will be present.
121 Before using the contents of the response, the gssapi-data should be
122 processed by gss_init_security_context to determine the state of the
123 security context. If this function indicates success, the response
124 can be used by the application. Otherwise an appropriate action
125 based on the authentication status should be.
127 For example the authentication could have failed on the final leg if
128 mutual authentication was requested and the server was not able to
129 prove its identity. In this case, the returned results are suspect.
130 It is not always possible to mutually authenticate the server before
131 the HTTP operation. POST methods are in this category.
133 When the Kerberos Version 5 GSSAPI mechanism [5] is being used, the
134 HTTP server will be using a principal name of the form of
135 "HTTP/<hostname>".
137 4.2 The Authorization Request Header
139 Upon receipt of the response containing a "WWW-Authenticate" header
140 from the server, the client is expected to retry the HTTP request,
141 passing a HTTP "Authorization" header line. This is defined
142 according to the framework described in [1] utilized as follows:
144 credentials = "Negotiate" auth-data2
145 auth-data2 = 1#( gssapi-data )
147 gssapi-data
148 This directive contains is the base64 encoding of an
149 InitialContextToken as defined in [3].
151 Any returned code other than a success 2xx code represents an
152 authentication error. If a 401 containing a "WWW-Authenticate"
153 header with "Negotiate" and gssapi-data is returned from the server,
154 it is a continuation of the authentication request.
156 A client may initiate a connection to the server with an
157 "Authorization" header containing the initial token for the server.
158 This form will bypass the initial 401 error from the server when the
159 client knows that the server will accept the Negotiate HTTP
160 authentication type.
162 5. Negotiate Operation Example
164 The client requests an access-protected document from server via a
165 GET method request. The URI of the document is
166 "http://www.nowhere.org/dir/index.html".
168 C: GET dir/index.html
170 The first time the client requests the document, no Authorization
171 header is sent, so the server responds with:
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177 S: HTTP/1.1 401 Unauthorized
178 S: WWW-Authenticate: Negotiate
180 The client will obtain the user credentials using the SPNEGO GSSAPI
181 mechanism type to identify generate a GSSAPI message to be sent to
182 the server with a new request, including the following Authorization
183 header:
185 C: GET dir/index.html
186 C: Authorization: Negotiate a87421000492aa874209af8bc028
188 The server will decode the gssapi-data and pass this to the SPNEGO
189 GSSAPI mechanism in the gss_accept_security_context function. If the
190 context is not complete, the server will respond with a 401 status
191 code with a WWW-Authenticate header containing the gssapi-data.
193 S: HTTP/1.1 401 Unauthorized
194 S: WWW-Authenticate: Negotiate 749efa7b23409c20b92356
196 The client will decode the gssapi-data and pass this into
197 gss_init_security_context and return the new gssapi-data to the
198 server.
200 C: GET dir/index.html
201 C: Authorization: Negotiate 89a8742aa8729a8b028
203 This cycle can continue until the security context is complete.
205 When the return value from the gss_accept_security_context function
206 indicates that the security context is complete, it may supply final
207 authentication data to be returned to the client. If the server has
208 more gssapi data to send to the client to complete the context it is
209 to be carried in WWW-Authenticate header with the final response
210 containing the HTTP body.
212 S: HTTP/1.1 200 Success
213 S: WWW-Authenticate: Negotiate ade0234568a4209af8bc0280289eca
215 The client will decode the gssapi-data and supply it to
216 gss_init_security_context using the context for this server. If the
217 status is successful from the final gss_init_security_context, the
218 response can be used by the application.
220 7. Security Considerations
222 The SPNEGO HTTP authentication facility is only used to provide
223 authentication of a user to server. It provides no facilities for
224 protecting the HTTP headers or data including the Authorization and
225 WWW-Authenticate headers that are used to implement this mechanism.
227 This mechanism is not used for HTTP authentication to HTTP proxies.
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234 If an HTTP proxy is used between the client and server, it must take
235 care to not share authenticated connections between different
236 authenticated clients to the same server. If this is not honored,
237 then the server can easily lose track of security context
238 associations. A proxy that correctly honors client to server
239 authentication integrity will supply the "Proxy-support: Session-
240 Based-Authentication" HTTP header to the client in HTTP responses
241 from the proxy. The client MUST NOT utilize the SPNEGO HTTP
242 authentication mechanism through a proxy unless the proxy supplies
243 this header with the "401 Unauthorized" response from the server.
245 When using the SPNEGO HTTP authentication facility with client
246 supplied data such as PUT and POST, the authentication should be
247 complete between the client and server before sending the user data.
248 The return status from the gss_init_security_context will indicate
249 with the security context is complete. At this point the data can be
250 sent to the server.
253 8. References
257 10. Author's Addresses
259 John Brezak
260 Microsoft
261 One Microsoft Way
262 Redmond, Washington
263 Email: jbrezak@microsoft.com
289 Brezak Category - Informational 5 \f
290 HTTP Kerberos Access Authentication November 2003
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347 Brezak Category - Informational 6 \f