One document matched: draft-ietf-kitten-sasl-saml-ec-04.txt
Differences from draft-ietf-kitten-sasl-saml-ec-03.txt
Network Working Group S. Cantor
Internet-Draft Shibboleth Consortium
Intended status: Standards Track S. Josefsson
Expires: April 20, 2013 SJD AB
October 17, 2012
SAML Enhanced Client SASL and GSS-API Mechanisms
draft-ietf-kitten-sasl-saml-ec-04.txt
Abstract
Security Assertion Markup Language (SAML) 2.0 is a generalized
framework for the exchange of security-related information between
asserting and relying parties. Simple Authentication and Security
Layer (SASL) and the Generic Security Service Application Program
Interface (GSS-API) are application frameworks to facilitate an
extensible authentication model. This document specifies a SASL and
GSS-API mechanism for SAML 2.0 that leverages the capabilities of a
SAML-aware "enhanced client" to address significant barriers to
federated authentication in a manner that encourages reuse of
existing SAML bindings and profiles designed for non-browser
scenarios.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on April 20, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
Cantor & Josefsson Expires April 20, 2013 [Page 1]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Applicability for Non-HTTP Use Cases . . . . . . . . . . . . . 6
4. SAML SASL Mechanism Specification . . . . . . . . . . . . . . 9
4.1. Advertisement . . . . . . . . . . . . . . . . . . . . . . 9
4.2. Initiation . . . . . . . . . . . . . . . . . . . . . . . . 9
4.3. Server Response . . . . . . . . . . . . . . . . . . . . . 10
4.4. User Authentication with Identity Provider . . . . . . . . 10
4.5. Client Response . . . . . . . . . . . . . . . . . . . . . 10
4.6. Outcome . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.7. Additional Notes . . . . . . . . . . . . . . . . . . . . . 10
5. SAML EC GSS-API Mechanism Specification . . . . . . . . . . . 12
5.1. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 12
5.2. Session Key Derivation . . . . . . . . . . . . . . . . . . 13
5.2.1. Generated by Identity Provider . . . . . . . . . . . . 13
5.2.2. Derived Session Keys . . . . . . . . . . . . . . . . . 14
5.3. Per-Message Tokens . . . . . . . . . . . . . . . . . . . . 14
5.4. Pseudo-Random Function (PRF) . . . . . . . . . . . . . . . 15
5.5. GSS-API Principal Name Types for SAML EC . . . . . . . . . 15
5.5.1. User Naming Considerations . . . . . . . . . . . . . . 16
5.5.2. Service Naming Considerations . . . . . . . . . . . . 16
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 26
7.1. Risks Left Unaddressed . . . . . . . . . . . . . . . . . . 26
7.2. User Privacy . . . . . . . . . . . . . . . . . . . . . . . 26
7.3. Collusion between RPs . . . . . . . . . . . . . . . . . . 27
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
8.1. GSS-API and SASL Mechanism Registration . . . . . . . . . 28
8.2. XML Namespace Name for SAML-EC . . . . . . . . . . . . . . 28
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.1. Normative References . . . . . . . . . . . . . . . . . . . 29
9.2. Normative References for GSS-API Implementers . . . . . . 30
9.3. Informative References . . . . . . . . . . . . . . . . . . 31
Appendix A. Appendix A. XML Schema . . . . . . . . . . . . . . . 32
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . . 34
Appendix C. Changes . . . . . . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36
Cantor & Josefsson Expires April 20, 2013 [Page 2]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
1. Introduction
Security Assertion Markup Language (SAML) 2.0
[OASIS.saml-core-2.0-os] is a modular specification that provides
various means for a user to be identified to a relying party (RP)
through the exchange of (typically signed) assertions issued by an
identity provider (IdP). It includes a number of protocols, protocol
bindings [OASIS.saml-bindings-2.0-os], and interoperability profiles
[OASIS.saml-profiles-2.0-os] designed for different use cases.
Additional profiles and extensions are also routinely developed and
published.
Simple Authentication and Security Layer (SASL) [RFC4422] is a
generalized mechanism for identifying and authenticating a user and
for optionally negotiating a security layer for subsequent protocol
interactions. SASL is used by application protocols like IMAP, POP
and XMPP [RFC3920]. The effect is to make authentication modular, so
that newer authentication mechanisms can be added as needed.
The Generic Security Service Application Program Interface (GSS-API)
[RFC2743] provides a framework for applications to support multiple
authentication mechanisms through a unified programming interface.
This document defines a pure SASL mechanism for SAML, but it conforms
to the bridge between SASL and the GSS-API called GS2 [RFC5801].
This means that this document defines both a SASL mechanism and a
GSS-API mechanism. The GSS-API interface is optional for SASL
implementers, and the GSS-API considerations can be avoided in
environments that uses SASL directly without GSS-API.
The mechanisms specified in this document allow a SASL- or GSS-API-
enabled server to act as a SAML relying party, or service provider
(SP), by advertising this mechanism as an option for SASL or GSS-API
clients that support the use of SAML to communicate identity and
attribute information. Clients supporting this mechanism are termed
"enhanced clients" in SAML terminology because they understand the
federated authentication model and have specific knowledge of the
IdP(s) associated with the user. This knowledge, and the ability to
act on it, addresses a significant problem with browser-based SAML
profiles known as the "discovery", or "where are you from?" (WAYF)
problem. Obviating the need for the RP to interact with the client
to determine the right IdP (and its network location) is both a user
interface and security improvement.
The SAML mechanism described in this document is an adaptation of an
existing SAML profile, the Enhanced Client or Proxy (ECP) Profile
(V2.0) [SAMLECP20], and therefore does not establish a separate
authentication, integrity and confidentiality mechanism. It is
anticipated that existing security layers, such as Transport Layer
Cantor & Josefsson Expires April 20, 2013 [Page 3]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
Security (TLS) or Secure Shell (SSH), will continued to be used.
Figure 1 describes the interworking between SAML and SASL: this
document requires enhancements to the RP and to the client (as the
two SASL communication endpoints) but no changes to the SAML IdP are
assumed apart from its support for the applicable SAML profile. To
accomplish this, a SAML protocol exchange between the RP and the IdP,
brokered by the client, is tunneled within SASL. There is no assumed
communication between the RP and the IdP, but such communication may
occur in conjunction with additional SAML-related profiles not in
scope for this document.
+-----------+
| SAML |
| Relying |
| Party |
| |
+-----------+
^
+--|--+
| S| |
S | A| |
A | M| |
S | L| |
L | | |
| | |
+--|--+
+------------+ v
| | +----------+
| SAML | SAML SOAP | |
| Identity |<--------------->| Client |
| Provider | Binding | |
+------------+ +----------+
Figure 1: Interworking Architecture
Cantor & Josefsson Expires April 20, 2013 [Page 4]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
2. Terminology
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 [RFC2119].
The reader is also assumed to be familiar with the terms used in the
SAML 2.0 specification, and an understanding of the Enhanced Client
or Proxy (ECP) Profile (V2.0) [SAMLECP20] is necessary, as part of
this mechanism explicitly reuses and references it.
This document can be implemented without knowledge of GSS-API since
the normative aspects of the GS2 protocol syntax have been duplicated
in this document. The document may also be implemented to provide a
GSS-API mechanism, and then knowledge of GSS-API is essential. To
faciliate these two variants, the references has been split into two
parts, one part that provides normative references for all readers,
and one part that adds additional normative references required for
implementers that wish to implement the GSS-API portion.
Cantor & Josefsson Expires April 20, 2013 [Page 5]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
3. Applicability for Non-HTTP Use Cases
While SAML is designed to support a variety of application scenarios,
the profiles for authentication defined in the original standard are
designed around HTTP [RFC2616] applications. They are not, however,
limited to browsers, because it was recognized that browsers suffer
from a variety of functional and security deficiencies that would be
useful to avoid where possible. Specifically, the notion of an
"Enhanced Client" (or a proxy acting as one on behalf of a browser,
thus the term "ECP") was specified for a software component that acts
somewhat like a browser from an application perspective, but includes
limited, but sufficient, awareness of SAML to play a more conscious
role in the authentication exchange between the RP and the IdP. What
follows is an outline of the Enhanced Client or Proxy (ECP) Profile
(V2.0) [SAMLECP20], as applied to the web/HTTP service use case:
1. The Enhanced Client requests a resource of a Relying Party (RP)
(via an HTTP request). In doing so, it advertises its "enhanced"
capability using HTTP headers.
2. The RP, desiring SAML authentication and noting the client's
capabilities, responds not with an HTTP redirect or form, but
with a SOAP [W3C.soap11] envelope containing a SAML
<AuthnRequest> along with some supporting headers. This request
identifies the RP (and may be signed), and may provide hints to
the client as to what IdPs the RP finds acceptable, but the
choice of IdP is generally left to the client.
3. The client is then responsible for delivering the body of the
SOAP message to the IdP it is instructed to use (often via
configuration ahead of time). The user authenticates to the IdP
ahead of, during, or after the delivery of this message, and
perhaps explicitly authorizes the response to the RP.
4. Whether authentication succeeds or fails, the IdP responds with
its own SOAP envelope, generally containing a SAML <Response>
message for delivery to the RP. In a successful case, the
message will include a SAML <Assertion> containing
authentication, and possibly attribute, information about the
user. Either the response or assertion alone is signed, and the
assertion may be encrypted to a key negotiated with or known to
belong to the RP.
5. The client then delivers the SOAP envelope containing the
<Response> to the RP at a location the IdP directs (which acts as
an additional, though limited, defense against MITM attacks).
This completes the SAML exchange.
Cantor & Josefsson Expires April 20, 2013 [Page 6]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
6. The RP now has sufficient identity information to approve the
original HTTP request or not, and acts accordingly. Everything
between the original request and this response can be thought of
as an "interruption" of the original HTTP exchange.
When considering this flow in the context of an arbitrary application
protocol and SASL, the RP and the client both must change their code
to implement this SASL mechanism, but the IdP can remain untouched.
The existing RP/client exchange that is tunneled through HTTP maps
well to the tunneling of that same exchange in SASL. In the parlance
of SASL [RFC4422], this mechanism is "client-first" for consistency
with GS2. The steps are shown below:
1. The server MAY advertise the SAML20EC and/or SAML20EC-PLUS
mechanisms.
2. The client initiates a SASL authentication with SAML20EC or
SAML20EC-PLUS.
3. The server sends the client a challenge consisting of a SOAP
envelope containing its SAML <AuthnRequest>.
4. The SASL client unpacks the SOAP message and communicates with
its chosen IdP to relay the SAML <AuthnRequest> to it. This
communication, and the authentication with the IdP, proceeds
separately from the SASL process.
5. Upon completion of the exchange with the IdP, the client responds
to the SASL server with a SOAP envelope containing the SAML
<Response> it obtained, or a SOAP fault, as warranted.
6. The SASL Server indicates success or failure.
Note: The details of the SAML processing, which are consistent with
the Enhanced Client or Proxy (ECP) Profile (V2.0) [SAMLECP20], are
such that the client MUST interact with the IdP in order to complete
any SASL exchange with the RP. The assertions issued by the IdP for
the purposes of the profile, and by extension this SASL mechanism,
are short lived, and therefore cannot be cached by the client for
later use.
Encompassed in step four is the client-driven selection of the IdP,
authentication to it, and the acquisition of a response to provide to
the SASL server. These processes are all external to SASL.
With all of this in mind, the typical flow appears as follows:
Cantor & Josefsson Expires April 20, 2013 [Page 7]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
SASL Serv. Client IdP
|>-----(1)----->| | Advertisement
| | |
|<-----(2)-----<| | Initiation
| | |
|>-----(3)----->| | SASL Server Response
| | |
| |<- - -(4)- - >| SOAP AuthnRequest + user authn
| | |
|<-----(5)-----<| | SASL Client Response
| | |
|>-----(6)----->| | Server sends Outcome
| | |
----- = SASL
- - - = SOAP over HTTPS (external to SASL)
Figure 2: Authentication flow
Cantor & Josefsson Expires April 20, 2013 [Page 8]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
4. SAML SASL Mechanism Specification
Based on the previous figures, the following operations are defined
by the SAML SASL mechanism:
4.1. Advertisement
To advertise that a server supports this mechanism, during
application session initiation, it displays the name "SAML20EC"
and/or "SAML20EC-PLUS" in the list of supported SASL mechanisms
(depending on its support for channel binding).
4.2. Initiation
A client initiates "SAML20EC" or "SAML20EC-PLUS" authentication. If
supported by the application protocol, the client MAY include an
initial response, otherwise it waits until the server has issued an
empty challenge (because the mechanism is client-first).
The format of the initial client response is as follows:
hok = "urn:oasis:names:tc:SAML:2.0:cm:holder-of-key"
mutual = "urn:oasis:names:tc:SAML:2.0:profiles:SSO:ecp:2.0:" \
"WantAuthnRequestsSigned"
initial-resp = gs2-cb-flag "," [gs2-authzid] "," [hok] "," [mutual]
The gs2-cb-flag MUST be set as defined in [RFC5801] to indicate
whether the client supports channel binding. This takes the place of
the PAOS HTTP header extension used in [SAMLECP20] to indicate
channel binding support.
The optional "gs2-authzid" field holds the authorization identity, as
requested by the client.
The optional "hok" field is a constant that signals the client's
support for stronger security by means of a locally held key. This
takes the place of the PAOS HTTP header extension used in [SAMLECP20]
to indicate "holder of key" support.
The optional "mutual" field is a constant that signals the client's
desire for mutual authentication. If set, the SASL server MUST
digitally sign its SAML <AuthnRequest> message. The URN constant
above is a single string; the linefeed is shown for RFC formatting
reasons.
Cantor & Josefsson Expires April 20, 2013 [Page 9]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
4.3. Server Response
The SASL server responds with a SOAP envelope constructed in
accordance with section 2.3.2 of [SAMLECP20]. This includes adhering
to the SOAP header requirements of the SAML PAOS Binding
[OASIS.saml-bindings-2.0-os], for compatibility with the existing
profile. Various SOAP headers are also consumed by the client in
exactly the same manner prescribed by that section.
4.4. User Authentication with Identity Provider
Upon receipt of the Server Response (Section 4.3), the steps
described in sections 2.3.3 through 2.3.6 of [SAMLECP20] are
performed between the client and the chosen IdP. The means by which
the client determines the IdP to use, and where it is located, are
out of scope of this mechanism.
The exact means of authentication to the IdP are also out of scope,
but clients supporting this mechanism MUST support HTTP Basic
Authentication as defined in [RFC2617] and TLS client authentication
as defined in [RFC5246].
4.5. Client Response
Assuming a response is obtained from the IdP, the client responds to
the SASL server with a SOAP envelope constructed in accordance with
section 2.3.7 of [SAMLECP20]. This includes adhering to the SOAP
header requirements of the SAML PAOS Binding
[OASIS.saml-bindings-2.0-os], for compatibility with the existing
profile. If the client is unable to obtain a response from the IdP,
it responds to the SASL server with a SOAP envelope containing a SOAP
fault.
4.6. Outcome
The SAML protocol exchange having completed, the SASL server will
transmit the outcome to the client depending on local validation of
the client responses. This outcome is transmitted in accordance with
the application protocol in use.
4.7. Additional Notes
Because this mechanism is an adaptation of an HTTP-based profile,
there are a few requirements outlined in [SAMLECP20] that make
reference to a response URL that is normally used to regulate where
the client returns information to the RP. There are also security-
related checks built into the profile that involve this location.
Cantor & Josefsson Expires April 20, 2013 [Page 10]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
For compatibility with existing IdP and profile behavior, and to
provide for mutual authentication, the SASL server MUST populate the
responseConsumerURL and AssertionConsumerServiceURL attributes with
its service name. The parties then perform the steps described in
[SAMLECP20] as usual.
Similarly, the use of HTTP status signaling between the RP and client
mandated by [SAMLECP20] may not be applicable.
Cantor & Josefsson Expires April 20, 2013 [Page 11]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
5. SAML EC GSS-API Mechanism Specification
This section and its sub-sections and all normative references of it
not referenced elsewhere in this document are INFORMATIONAL for SASL
implementors, but they are NORMATIVE for GSS-API implementors.
The SAML SASL Enhanced Clients mechanism is also a GSS-API mechanism.
The messages are the same, but a) the GS2 header on the client's
first message is excluded when SAML EC is used as a GSS-API
mechanism, and b) the [RFC2743] section 3.1 initial context token
header is prefixed to the client's first authentication message
(context token).
The GSS-API mechanism OID for SAML EC is OID-TBD (IANA to assign: see
IANA considerations). The DER encoding of the OID is TBD.
The mutual_state request flag (GSS_C_MUTUAL_FLAG) MAY be set to TRUE,
resulting in the "mutual-auth" option set in the initial client
response. The security context mutual_state flag is set to TRUE only
if the server digitally signs its SAML <AuthnRequest> message, and
the identity provider signals this to the client in an <ecp:
RequestAuthenticated> SOAP header block.
If the mutual_state flag is not requested, or is not set, then the
security layer managed by the application outside of the GSS-API
mechanism is responsible for authenticating the acceptor. In this
case, applications MUST match the server identity from the existing
security layer with the target name. For TLS, this matching MUST be
performed as discussed in [RFC6125]. For SSH, this matching MUST be
performed as discussed in [RFC4462].
The lifetime of a security context established with this mechanism
SHOULD be limited by the value of a SessionNotOnOrAfter attribute, if
any, in the <AuthnStatement> of the SAML assertion received by the
RP.
SAML EC supports credential delegation through the issuance of SAML
assertions that the issuing identity provider will accept as proof of
authentication by a service on behalf of a user. Such assertions
MUST contain an <AudienceRestriction> condition element identifying
the identity provider, and a <SubjectConfirmation> element that the
acceptor can satisy. In such a case, the security context will have
its deleg_state flag (GSS_C_DELEG_FLAG) set to TRUE.
5.1. GSS-API Channel Binding
GSS-API channel binding [RFC5554] is a protected facility for
exchanging a cryptographic name for an enclosing channel between the
Cantor & Josefsson Expires April 20, 2013 [Page 12]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
initiator and acceptor. The initiator sends channel binding data and
the acceptor confirms that channel binding data has been checked.
The acceptor SHOULD accept any channel binding provided by the
initiator if null channel bindings are passed into
gss_accept_sec_context. Protocols such as HTTP Negotiate [RFC4559]
depend on this behavior of some Kerberos implementations.
The exchange and verification of channel binding information is
described by [SAMLECP20].
5.2. Session Key Derivation
Some GSS-API features (discussed in the following sections) require a
session key be established as a result of security context
establishment. In the common case of a "bearer" assertion in SAML,
there are a pair of approaches defined: exporting key material from
TLS and communicating a key to both parties via the identity
provider. Both are discussed below. In other cases such as
assertions based on "holder of key" confirmation bound to a client-
controlled key, there may be additional methods available.
Information defining or describing the session key, or a process for
deriving one, is communicated using a <samlec:SessionKey> element,
defined in the schema in Appendix A. This element can be used as a
SOAP header block or as an extension within a SAML assertion,
depending on the context of communication. The content of the
element further depends on the specific use in the mechanism and is
discussed below.
5.2.1. Generated by Identity Provider
The identity provider, if issuing a bearer assertion for use with
this mechanism, SHOULD provide a generated key for use by the
initiator and acceptor. This key is used as the protocol key for a
specific encryption type defined in accordance with [RFC3961]. The
key is base64-encoded and placed inside a <samlec:GeneratedKey>
element. The element's Algorithm XML attribute is set to the
encryption type name from the registry established by [RFC3961].
The <samlec:GeneratedKey> element is placed within a <samlec:
SessionKey> element, and this element is placed within the <saml:
Advice> element of the assertion issued. A copy of the element is
also added as a SOAP header block in the response from the identity
provider to the client.
The identity provider is left to determine which encryption type the
parties should use. It is unspecified how the initiator's
Cantor & Josefsson Expires April 20, 2013 [Page 13]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
capabilities are determined in this respect, but the acceptor MAY
indicate the algorithms it supports in its SAML metadata by means of
one or more <SessionKeyMethod> elements in an <samlmd:Extensions>
element, and an identity provider can leverage this information.
Multiple such extension elements may appear, in order of preference
by the acceptor.
All parties MUST support the "aes128-cts-hmac-sha1-96" encryption
type, defined by [RFC3962].
5.2.2. Derived Session Keys
In the event that a client is proving possession of a secret or
private key, a formal key agreement algorithm may be supported. For
example, if the server has an elliptic curve public key, the ECDH-ES
key agreement algorithm, as defined in [XMLENC11] may be used.
In such a case, the initiator communicates to the acceptor what
algorithm to use and any inputs to the process using a <SessionKey>
SOAP header block containing a <ds:KeyInfo> element, added to the
client response to the acceptor. The <ds:KeyInfo> element will
typically contain an <xenc11:DerivedKey> element conforming to
[XMLENC11]. The <ds:KeyInfo> element may also contain other
extensible content related to key establishment mechanisms defined
elsewhere.
5.3. Per-Message Tokens
The per-message tokens SHALL be the same as those for the Kerberos V5
GSS-API mechanism [RFC4121] (see Section 4.2 and sub-sections).
The replay_det_state (GSS_C_REPLAY_FLAG), sequence_state
(GSS_C_SEQUENCE_FLAG), conf_avail (GSS_C_CONF_FLAG) and integ_avail
(GSS_C_CONF_FLAG) security context flags are always set to TRUE.
The "protocol key" SHALL be a session key established in a manner
described in the previous section. "Specific keys" are then derived
as usual as described in Section 2 of [RFC4121], [RFC3961], and
[RFC3962].
The terms "protocol key" and "specific key" are Kerberos V5 terms
[RFC3961].
SAML20EC is PROT_READY as soon as the SAML response message has been
seen.
Cantor & Josefsson Expires April 20, 2013 [Page 14]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
5.4. Pseudo-Random Function (PRF)
The GSS-API has been extended with a Pseudo-Random Function (PRF)
interface in [RFC4401]. The purpose is to enable applications to
derive a cryptographic key from an established GSS-API security
context. This section defines a GSS_Pseudo_random that is applicable
for the SAML20EC GSS-API mechanism.
The GSS_Pseudo_random() [RFC4401] SHALL be the same as for the
Kerberos V5 GSS-API mechanism [RFC4402]. There is no acceptor-
asserted sub-session key, thus GSS_C_PRF_KEY_FULL and
GSS_C_PRF_KEY_PARTIAL are equivalent. The protocol key to be used
for the GSS_Pseudo_random() SHALL be the same as the key defined in
the previous section.
5.5. GSS-API Principal Name Types for SAML EC
Services that act as SAML relying parties are typically identified by
means of a URI called an "entityID". Clients that are named in the
<Subject> element of a SAML assertion are typically identified by
means of a <NameID> element, which is an extensible XML structure
containing, at minimum, an element value that names the subject and a
Format attribute.
In practice, a GSS-API client and server are unlikely to know in
advance the name of the initiator as it will be expressed by the SAML
identity provider upon completion of authentication. It is also
generally incorrect to assume that a particular acceptor name will
directly map into a particular RP entityID, because there is often a
layer of naming indirection between particular services on hosts and
the identity of a relying party in SAML terms.
To avoid complexity, and avoid unnecessary use of XML within the
naming layer, the SAML EC mechanism relies on the common/expected
name types used for acceptors and initiators,
GSS_C_NT_HOSTBASED_SERVICE and GSS_C_NT_USER_NAME. The mechanism
provides for validation of the host-based service name in conjunction
with the SAML exchange. It does not attempt to solve the problem of
mapping between an initiator "username", the user's identity while
authenticating to the identity provider, and the information supplied
by the identity provider to the acceptor. These relationships must
be managed through local policy at the initiator and acceptor.
SAML-based information associated with the initiator SHOULD be
expressed to the acceptor using GSS-API naming extensions
[I-D.ietf-kitten-gssapi-naming-exts], in accordance with
[I-D.ietf-abfab-gss-eap-naming].
Cantor & Josefsson Expires April 20, 2013 [Page 15]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
5.5.1. User Naming Considerations
The GSS_C_NT_USER_NAME form represents the name of an individual
user. Clients often rely on this value to determine the appropriate
credentials to use in authenticating to the identity provider, and
supply it to the server for use by the acceptor.
Upon successful completion of this mechanism, the server MUST
construct the authenticated initiator name based on the <saml:NameID>
element in the assertion it successfully validated. The name is
constructed as a UTF-8 string in the following form:
name = element-value "!" Format "!" NameQualifier
"!" SPNameQualifier "!" SPProvidedID
The "element-value" token refers to the content of the <saml:NameID>
element. The other tokens refer to the identically named XML
attributes defined for use with the element. If an attribute is not
present, which is common, it is omitted (i.e., replaced with the
empty string). The Format value is never omitted; if not present,
the SAML-equivalent value of
"urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified" is used.
Not all SAML assertions contain a <saml:NameID> element. In the
event that no such element is present, including the exceptional
cases of a <saml:BaseID> element or a <saml:EncryptedID> element that
cannot be decrypted, the GSS_C_NT_ANONYMOUS name type MUST be used
for the initiator name.
As noted in the previous section, it is expected that most
applications able to rely on SAML authentication would make use of
naming extensions to obtain additional information about the user
based on the assertion. This is particularly true in the anonymous
case, or in cases in which the SAML name is pseudonymous or transient
in nature. The ability to express the SAML name in
GSS_C_NT_USER_NAME form is intended for compatibility with
applications that cannot make use of additional information.
5.5.2. Service Naming Considerations
The GSS_C_NT_HOSTBASED_SERVICE name form represents a service running
on a host; it is textually represented as "service@host". This name
form is required by most SASL profiles and is used by many existing
applications that use the Kerberos GSS-API mechanism. Such a name is
used directly by this mechanism as the effective
AssertionConsumerService of the server.
This value is used in the construction of the responseConsumerURL and
Cantor & Josefsson Expires April 20, 2013 [Page 16]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
AssertionConsumerServiceURL attributes, and for eventual comparison
and validation by the client before completing the exchange. The
value MUST be securely associated with the SAML entityID claimed by
the server by the identity provider, such as through the use of SAML
metadata [OASIS.saml-metadata-2.0-os].
Cantor & Josefsson Expires April 20, 2013 [Page 17]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
6. Example
Suppose the user has an identity at the SAML IdP saml.example.org and
a Jabber Identifier (jid) "somenode@example.com", and wishes to
authenticate his XMPP connection to xmpp.example.com (and example.com
and example.org have established a SAML-capable trust relationship).
The authentication on the wire would then look something like the
following:
Step 1: Client initiates stream to server:
<stream:stream xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='example.com' version='1.0'>
Step 2: Server responds with a stream tag sent to client:
<stream:stream
xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams'
id='some_id' from='example.com' version='1.0'>
Step 3: Server informs client of available authentication mechanisms:
<stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
<mechanism>SAML20EC</mechanism>
</mechanisms>
</stream:features>
Step 4: Client selects an authentication mechanism and sends the
initial client response (it is base64 encoded as specified by the
XMPP SASL protocol profile):
<auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl' mechanism='SAML20EC'>
biwsLA==
</auth>
The initial response is "n,," which signals that channel binding is
Cantor & Josefsson Expires April 20, 2013 [Page 18]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
not used, there is no authorization identity, and the client does not
support key-based confirmation or want mutual authentication.
Step 5: Server sends a challenge to client in the form of a SOAP
envelope containing its SAML <AuthnRequest>:
<challenge xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>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</challenge>
The Base64 [RFC4648] decoded envelope:
Cantor & Josefsson Expires April 20, 2013 [Page 19]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
<S:Envelope
xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion"
xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"
xmlns:S="http://schemas.xmlsoap.org/soap/envelope/">
<S:Header>
<paos:Request xmlns:paos="urn:liberty:paos:2003-08"
messageID="c3a4f8b9c2d" S:mustUnderstand="1"
S:actor="http://schemas.xmlsoap.org/soap/actor/next"
responseConsumerURL="xmpp@xmpp.example.com"
service="urn:oasis:names:tc:SAML:2.0:profiles:SSO:ecp"/>
<ecp:Request
xmlns:ecp="urn:oasis:names:tc:SAML:2.0:profiles:SSO:ecp"
S:actor="http://schemas.xmlsoap.org/soap/actor/next"
S:mustUnderstand="1" ProviderName="Jabber at example.com">
<saml:Issuer>https://xmpp.example.com</saml:Issuer>
</ecp:Request>
</S:Header>
<S:Body>
<samlp:AuthnRequest
ID="c3a4f8b9c2d" Version="2.0" IssueInstant="2007-12-10T11:39:34Z"
ProtocolBinding="urn:oasis:names:tc:SAML:2.0:bindings:PAOS"
AssertionConsumerServiceURL="xmpp@xmpp.example.com">
<saml:Issuer xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">
https://xmpp.example.com
</saml:Issuer>
<samlp:NameIDPolicy AllowCreate="true"
Format="urn:oasis:names:tc:SAML:2.0:nameid-format:persistent"/>
<samlp:RequestedAuthnContext Comparison="exact">
<saml:AuthnContextClassRef>
urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport
</saml:AuthnContextClassRef>
</samlp:RequestedAuthnContext>
</samlp:AuthnRequest>
</S:Body>
</S:Envelope>
Step 5 (alt): Server returns error to client:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<incorrect-encoding/>
</failure>
</stream:stream>
Step 6: Client relays the request to IdP in a SOAP message
transmitted over HTTP (over TLS). HTTP portion not shown, use of
Cantor & Josefsson Expires April 20, 2013 [Page 20]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
Basic Authentication is assumed. The body of the SOAP envelope is
exactly the same as received in the previous step.
<S:Envelope
xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion"
xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"
xmlns:S="http://schemas.xmlsoap.org/soap/envelope/">
<S:Body>
<samlp:AuthnRequest>
<!-- same as above -->
</samlp:AuthnRequest>
</S:Body>
</S:Envelope>
Step 7: IdP responds to client with a SOAP response containing a SAML
<Response> containing a short-lived SSO assertion (shown as an
encrypted variant in the example). A session key is included in the
assertion and in a header for the client.
Cantor & Josefsson Expires April 20, 2013 [Page 21]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
<S:Envelope
xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion"
xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"
xmlns:S="http://schemas.xmlsoap.org/soap/envelope/">
<S:Header>
<ecp:Response S:mustUnderstand="1"
S:actor="http://schemas.xmlsoap.org/soap/actor/next"
AssertionConsumerServiceURL="xmpp@xmpp.example.com"/>
<samlec:SessionKey xmlns:samlec="urn:ietf:params:xml:ns:samlec">
<samlec:GeneratedKey Algorithm="aes128-cts-hmac-sha1-96">
3w1wSBKUosRLsU69xGK7dg==
</samlec:GeneratedKey>
</samlec:SessionKey>
</S:Header>
<S:Body>
<samlp:Response ID="d43h94r389309r" Version="2.0"
IssueInstant="2007-12-10T11:42:34Z" InResponseTo="c3a4f8b9c2d"
Destination="xmpp@xmpp.example.com">
<saml:Issuer>https://saml.example.org</saml:Issuer>
<samlp:Status>
<samlp:StatusCode
Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>
</samlp:Status>
<saml:EncryptedAssertion>
<!-- contents elided, has copy of session key in Advice -->
</saml:EncryptedAssertion>
</samlp:Response>
</S:Body>
</S:Envelope>
Step 8: Client sends SOAP envelope containing the SAML <Response> as
a response to the SASL server's challenge:
Cantor & Josefsson Expires April 20, 2013 [Page 22]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
<response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>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</response>
The Base64 [RFC4648] decoded envelope:
<S:Envelope
xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion"
xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"
xmlns:S="http://schemas.xmlsoap.org/soap/envelope/">
<S:Header>
<paos:Response xmlns:paos="urn:liberty:paos:2003-08"
S:actor="http://schemas.xmlsoap.org/soap/actor/next"
S:mustUnderstand="1" refToMessageID="6c3a4f8b9c2d"/>
</S:Header>
<S:Body>
<samlp:Response ID="d43h94r389309r" Version="2.0"
IssueInstant="2007-12-10T11:42:34Z" InResponseTo="c3a4f8b9c2d"
Destination="xmpp@xmpp.example.com">
<saml:Issuer>https://saml.example.org</saml:Issuer>
<samlp:Status>
<samlp:StatusCode
Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>
</samlp:Status>
<saml:EncryptedAssertion>
<!-- contents elided, has copy of session key in Advice -->
</saml:EncryptedAssertion>
</samlp:Response>
</S:Body>
Cantor & Josefsson Expires April 20, 2013 [Page 23]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
</S:Envelope>
Step 9: Server informs client of successful authentication:
<success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Step 9 (alt): Server informs client of failed authentication:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<temporary-auth-failure/>
</failure>
</stream:stream>
Step 10: Client initiates a new stream to server:
<stream:stream xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='example.com' version='1.0'>
Step 11: Server responds by sending a stream header to client along
with any additional features (or an empty features element):
<stream:stream xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='c2s_345' from='example.com' version='1.0'>
<stream:features>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/>
<session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
</stream:features>
Step 12: Client binds a resource:
<iq type='set' id='bind_1'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<resource>someresource</resource>
</bind>
</iq>
Cantor & Josefsson Expires April 20, 2013 [Page 24]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
Step 13: Server informs client of successful resource binding:
<iq type='result' id='bind_1'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<jid>somenode@example.com/someresource</jid>
</bind>
</iq>
Please note: line breaks were added to the base64 for clarity.
Cantor & Josefsson Expires April 20, 2013 [Page 25]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
7. Security Considerations
This section will address only security considerations associated
with the use of SAML with SASL applications. For considerations
relating to SAML in general, the reader is referred to the SAML
specification and to other literature. Similarly, for general SASL
Security Considerations, the reader is referred to that
specification.
Version 2.0 of the Enhanced Client or Proxy Profile [SAMLECP20] adds
optional support for channel binding and use of "Holder of Key"
subject confirmation. The former is strongly recommended for use
with this mechanism to detect "Man in the Middle" attacks between the
client and the RP without relying on flawed commercial TLS
infrastructure. The latter may be impractical in many cases, but is
a valuable way of strengthening client authentication, protecting
against phishing, and improving the overall mechanism.
7.1. Risks Left Unaddressed
The adaptation of a web-based profile that is largely designed around
security-oblivious clients and a bearer model for security token
validation results in a number of basic security exposures that
should be weighed against the compatibility and client simplification
benefits of this mechanism.
When channel binding is not used, protection against "Man in the
Middle" attacks is left to lower layer protocols such as TLS, and the
development of user interfaces able to implement that has not been
effectively demonstrated. Failure to detect a MITM can result in
phishing of the user's credentials if the attacker is between the
client and IdP, or the theft and misuse of a short-lived credential
(the SAML assertion) if the attacker is able to impersonate a RP.
SAML allows for source address checking as a minor mitigation to the
latter threat, but this is often impractical. IdPs can mitigate to
some extent the exposure of personal information to RP attackers by
encrypting assertions with authenticated keys.
7.2. User Privacy
The IdP is aware of each RP that a user logs into. There is nothing
in the protocol to hide this information from the IdP. It is not a
requirement to track the activity, but there is nothing technically
that prohibits the collection of this information. Servers should be
aware that SAML IdPs will track - to some extent - user access to
their services. This exposure extends to the use of session keys
generated by the IdP to secure messages between the parties.
Cantor & Josefsson Expires April 20, 2013 [Page 26]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
It is also out of scope of the mechanism to determine under what
conditions an IdP will release particular information to a relying
party, and it is generally unclear in what fashion user consent could
be established in real time for the release of particular
information. The SOAP exchange with the IdP does not preclude such
interaction, but neither does it define that interoperably.
7.3. Collusion between RPs
Depending on the information supplied by the IdP, it may be possible
for RPs to correlate data that they have collected. By using the
same identifier to log into every RP, collusion between RPs is
possible. SAML supports the notion of pairwise, or targeted/
directed, identity. This allows the IdP to manage opaque, pairwise
identifiers for each user that are specific to each RP. However,
correlation is often possible based on other attributes supplied, and
is generally a topic that is beyond the scope of this mechanism. It
is sufficient to say that this mechanism does not introduce new
correlation opportunities over and above the use of SAML in web-based
use cases.
Cantor & Josefsson Expires April 20, 2013 [Page 27]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
8. IANA Considerations
8.1. GSS-API and SASL Mechanism Registration
The IANA is requested to assign a new entry for this GSS mechanism in
the sub-registry for SMI Security for Mechanism Codes, whose prefix
is iso.org.dod.internet.security.mechanisms (1.3.6.1.5.5) and to
reference this specification in the registry.
The IANA is requested to register the following SASL profile:
SASL mechanism profiles: SAML20EC and SAML20EC-PLUS
Security Considerations: See this document
Published Specification: See this document
For further information: Contact the authors of this document.
Owner/Change controller: the IETF
Note: None
8.2. XML Namespace Name for SAML-EC
A URN sub-namespace for XML constructs introduced by this mechanism
is defined as follows:
URI: urn:ietf:params:xml:ns:samlec
Specification: See Appendix A of this document.
Description: This is the XML namespace name for XML constructs
introduced by the SAML Enhanced Client SASL and GSS-API Mechanisms.
Registrant Contact: the IESG
Cantor & Josefsson Expires April 20, 2013 [Page 28]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
9. References
9.1. Normative References
[OASIS.saml-bindings-2.0-os]
Cantor, S., Hirsch, F., Kemp, J., Philpott, R., and E.
Maler, "Bindings for the OASIS Security Assertion Markup
Language (SAML) V2.0", OASIS
Standard saml-bindings-2.0-os, March 2005.
[OASIS.saml-core-2.0-os]
Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocol for the OASIS Security Assertion
Markup Language (SAML) V2.0", OASIS Standard saml-core-
2.0-os, March 2005.
[OASIS.saml-profiles-2.0-os]
Hughes, J., Cantor, S., Hodges, J., Hirsch, F., Mishra,
P., Philpott, R., and E. Maler, "Profiles for the OASIS
Security Assertion Markup Language (SAML) V2.0", OASIS
Standard OASIS.saml-profiles-2.0-os, March 2005.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[RFC4462] Hutzelman, J., Salowey, J., Galbraith, J., and V. Welch,
"Generic Security Service Application Program Interface
(GSS-API) Authentication and Key Exchange for the Secure
Shell (SSH) Protocol", RFC 4462, May 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Cantor & Josefsson Expires April 20, 2013 [Page 29]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
Security (TLS)", RFC 6125, March 2011.
[SAMLECP20]
Cantor, S., "SAML V2.0 Enhanced Client or Proxy Profile
Version 2.0", OASIS Working Draft OASIS.sstc-saml-ecp-
v2.0-wd06, October 2012.
[W3C.soap11]
Box, D., Ehnebuske, D., Kakivaya, G., Layman, A.,
Mendelsohn, N., Nielsen, H., Thatte, S., and D. Winer,
"Simple Object Access Protocol (SOAP) 1.1", W3C
Note soap11, May 2000, <http://www.w3.org/TR/SOAP/>.
9.2. Normative References for GSS-API Implementers
[I-D.ietf-abfab-gss-eap-naming]
Hartman, S. and J. Howlett, "Name Attributes for the GSS-
API EAP mechanism", draft-ietf-abfab-gss-eap-naming-06
(work in progress), October 2012.
[I-D.ietf-kitten-gssapi-naming-exts]
Williams, N., Johansson, L., Hartman, S., and S.
Josefsson, "GSS-API Naming Extensions",
draft-ietf-kitten-gssapi-naming-exts-15 (work in
progress), May 2012.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC3961] Raeburn, K., "Encryption and Checksum Specifications for
Kerberos 5", RFC 3961, February 2005.
[RFC3962] Raeburn, K., "Advanced Encryption Standard (AES)
Encryption for Kerberos 5", RFC 3962, February 2005.
[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.
[RFC4401] Williams, N., "A Pseudo-Random Function (PRF) API
Extension for the Generic Security Service Application
Program Interface (GSS-API)", RFC 4401, February 2006.
[RFC4402] Williams, N., "A Pseudo-Random Function (PRF) for the
Kerberos V Generic Security Service Application Program
Interface (GSS-API) Mechanism", RFC 4402, February 2006.
Cantor & Josefsson Expires April 20, 2013 [Page 30]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
[RFC5554] Williams, N., "Clarifications and Extensions to the
Generic Security Service Application Program Interface
(GSS-API) for the Use of Channel Bindings", RFC 5554,
May 2009.
[RFC5801] Josefsson, S. and N. Williams, "Using Generic Security
Service Application Program Interface (GSS-API) Mechanisms
in Simple Authentication and Security Layer (SASL): The
GS2 Mechanism Family", RFC 5801, July 2010.
[XMLENC11]
Hirsch, F. and T. Roessler, "XML Encryption Syntax and
Processing Version 1.1", W3C Editor's Draft W3C.xmlenc-
core-11-ed, September 2012.
9.3. Informative References
[OASIS.saml-metadata-2.0-os]
Cantor, S., Moreh, J., Philpott, R., and E. Maler,
"Metadata for the Security Assertion Markup Language
(SAML) V2.0", OASIS Standard saml-metadata-2.0-os,
March 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.
[RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004.
[RFC4559] Jaganathan, K., Zhu, L., and J. Brezak, "SPNEGO-based
Kerberos and NTLM HTTP Authentication in Microsoft
Windows", RFC 4559, June 2006.
[W3C.REC-xmlschema-1]
Thompson, H., Beech, D., Maloney, M., and N. Mendelsohn,
"XML Schema Part 1: Structures", W3C REC-xmlschema-1,
May 2001, <http://www.w3.org/TR/xmlschema-1/>.
Cantor & Josefsson Expires April 20, 2013 [Page 31]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
Appendix A. Appendix A. XML Schema
The following schema formally defines the
"urn:ietf:params:xml:ns:samlec" namespace used in this document, in
conformance with [W3C.REC-xmlschema-1] While XML validation is
optional, the schema that follows is the normative definition of the
constructs it defines. Where the schema differs from any prose in
this specification, the schema takes precedence.
Cantor & Josefsson Expires April 20, 2013 [Page 32]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
<schema
targetNamespace="urn:ietf:params:xml:ns:samlec"
xmlns="http://www.w3.org/2001/XMLSchema"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:S="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:samlec="urn:ietf:params:xml:ns:samlec"
elementFormDefault="unqualified"
attributeFormDefault="unqualified"
blockDefault="substitution"
version="1.0">
<import namespace="http://www.w3.org/2000/09/xmldsig#"/>
<import namespace="http://schemas.xmlsoap.org/soap/envelope/"/>
<element name="SessionKey" type="samlec:SessionKeyType"/>
<complexType name="SessionKeyType">
<choice>
<element ref="samlec:GeneratedKey"/>
<element ref="ds:KeyInfo"/>
</choice>
<attribute ref="S:mustUnderstand"/>
<attribute ref="S:actor"/>
</complexType>
<element name="GeneratedKey" type="samlec:GeneratedKeyType"/>
<complexType name="GeneratedKeyType">
<simpleContent>
<extension base="base64Binary">
<attribute name="Algorithm" type="string" use="required"/>
</extension>
</simpleContent>
</complexType>
<element name="SessionKeyMethod" type="samlec:SessionKeyMethodType"/>
<complexType name="SessionKeyMethodType">
<sequence>
<any namespace="##any" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</sequence>
<attribute name="Algorithm" type="anyURI" use="required"/>
</complexType>
</schema>
Cantor & Josefsson Expires April 20, 2013 [Page 33]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
Appendix B. Acknowledgments
The authors would like to thank Klaas Wierenga, Sam Hartman, Nico
Williams, and Jim Basney for their contributions.
Cantor & Josefsson Expires April 20, 2013 [Page 34]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
Appendix C. Changes
This section to be removed prior to publication.
o 04, stripped down the session key material to simplify it, and
define an IdP-brokered keying approach, moved session key XML
constructs from OASIS draft into this one
o 03, added TLS key export as a session key option, revised GSS
naming material based on list discussion
o 02, major revision of GSS-API material and updated references
o 01, SSH language added, noted non-assumption of HTTP error
handling, added guidance on life of security context.
o 00, Initial Revision, first WG-adopted draft. Removed support for
unsolicited SAML responses.
Cantor & Josefsson Expires April 20, 2013 [Page 35]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms October 2012
Authors' Addresses
Scott Cantor
Shibboleth Consortium
2740 Airport Drive
Columbus, Ohio 43219
United States
Phone: +1 614 247 6147
Email: cantor.2@osu.edu
Simon Josefsson
SJD AB
Hagagatan 24
Stockholm 113 47
SE
Email: simon@josefsson.org
URI: http://josefsson.org/
Cantor & Josefsson Expires April 20, 2013 [Page 36]
| PAFTECH AB 2003-2026 | 2026-04-23 11:21:04 |