[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]
Versions: 00 01
Network Working Group S. Cantor
Internet-Draft Internet2
Intended status: Standards Track S. Josefsson
Expires: September 3, 2011 SJD AB
March 2, 2011
SAML Enhanced Client SASL and GSS-API Mechanisms
draft-cantor-ietf-kitten-saml-ec-01.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 September 3, 2011.
Copyright Notice
Copyright (c) 2011 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 September 3, 2011 [Page 1]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
(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 . . . . . . . . . . . . . . . . . . . . . 9
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 . . . . . . . . . . . 11
5.1. GSS-API Principal Name Types for SAML EC . . . . . . . . . 11
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
7.1. Risks Left Unaddressed . . . . . . . . . . . . . . . . . . 19
7.2. User Privacy . . . . . . . . . . . . . . . . . . . . . . . 19
7.3. Collusion between RPs . . . . . . . . . . . . . . . . . . 20
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
9.1. Normative References . . . . . . . . . . . . . . . . . . . 22
9.2. Normative References for GSS-API Implementers . . . . . . 23
9.3. Informative References . . . . . . . . . . . . . . . . . . 23
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 24
Appendix B. Changes . . . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
Cantor & Josefsson Expires September 3, 2011 [Page 2]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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. We want to point out that 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 September 3, 2011 [Page 3]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
Security (TLS), 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 September 3, 2011 [Page 4]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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 September 3, 2011 [Page 5]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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
acted somewhat like a browser from an application perspective, but
included 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 in a new envelope 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 a new 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).
Cantor & Josefsson Expires September 3, 2011 [Page 6]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
This completes the SAML exchange.
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 client may accompany its "initial response" with a
SAML <Response> obtained from an IdP. 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. It MAY include a SAML <Response>.
3. The server sends the client one of two responses:
1. an indication of success or failure (if the client included a
SAML <Response>).
2. a challenge containing a SOAP envelope containing a SAML
<AuthnRequest>.
4. In the latter case, 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.
Cantor & Josefsson Expires September 3, 2011 [Page 7]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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:
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 (no initial response)
An alternative in which the client interacts with the IdP ahead of
time:
SASL Serv. Client IdP
|>-----(1)----->| | Advertisement
| | |
|<-----(2)-----<| | Initiation + Client Response
| | |
|>-----(3)----->| | Server sends Outcome
| | |
----- = SASL
Figure 3: Authentication flow (with initial response)
Cantor & Josefsson Expires September 3, 2011 [Page 8]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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:
saml-response = *%x00-FF
initial-response = gs2-cb-flag "," [gs2-authzid] "," [saml-response]
If the "saml-response" token is present, the client is attempting to
use a SAML <Response> negotiated earlier. In this case, the server's
next step is Outcome (Section 4.6).
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 used in [SAMLECP20] to indicate channel binding
support.
The optional "gs2-authzid" field holds the authorization identity, as
requested by the client.
4.3. Server Response
Assuming no SAML <Response> from the client, 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.
Cantor & Josefsson Expires September 3, 2011 [Page 9]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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 SHOULD support client
authentication via TLS 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.
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.
For compatibility with existing IdP and profile behavior, and to
provide for secure identification of the RP to the client, the SASL
server MUST populate responseConsumerURL and
AssertionConsumerServiceURL attributes with its service name,
expressed as an absolute URI. The parties then perform the steps
described in [SAMLECP20] as usual.
Cantor & Josefsson Expires September 3, 2011 [Page 10]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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 and channel binding data 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 1.3.6.1.4.1.11591.4.6.
SAML EC security contexts always have the mutual_state flag
(GSS_C_MUTUAL_FLAG) set to TRUE. SAML EC does not support credential
delegation, therefore SAML EC security contexts alway have the
deleg_state flag (GSS_C_DELEG_FLAG) set to FALSE.
The SAML EC mechanism does not support per-message tokens or
GSS_Pseudo_random.
5.1. GSS-API Principal Name Types for SAML EC
SAML EC supports standard generic name syntaxes for acceptors such as
GSS_C_NT_HOSTBASED_SERVICE (see [RFC2743], Section 4.1). These
service names MUST be associated with the SAML "entityID" claimed by
the RP, such as through the use of SAML metadata
[OASIS.saml-metadata-2.0-os].
SAML EC supports only a single name type for initiators:
GSS_C_NT_USER_NAME. GSS_C_NT_USER_NAME is the default name type for
SAML EC.
The query, display, and exported name syntaxes for SAML EC principal
names are all the same. There are no SAML EC-specific name syntaxes
-- applications should use generic GSS-API name types such as
GSS_C_NT_USER_NAME and GSS_C_NT_HOSTBASED_SERVICE (see [RFC2743],
Section 4). The exported name token does, of course, conform to
[RFC2743], Section 3.2, but the "NAME" part of the token should be
treated as a potential input string to the SAML EC name normalization
rules.
GSS-API name attributes may be defined in the future to hold the
normalized SAML EC Identifier.
Cantor & Josefsson Expires September 3, 2011 [Page 11]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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'>
biws
</auth>
The initial response is "n,," which signals that channel binding is
Cantor & Josefsson Expires September 3, 2011 [Page 12]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
not used, there is no authorization identity, and the client did not
provide a SAML <Response>.
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 September 3, 2011 [Page 13]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
<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 September 3, 2011 [Page 14]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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).
<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"/>
</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 -->
</saml:EncryptedAssertion>
</samlp:Response>
</S:Body>
</S:Envelope>
Step 8: Client sends SOAP envelope containing the SAML <Response> as
Cantor & Josefsson Expires September 3, 2011 [Page 15]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
a response to the SASL server's challenge:
<response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>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</response>
The Base64 [RFC4648] decoded envelope:
Cantor & Josefsson Expires September 3, 2011 [Page 16]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
<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 -->
</saml:EncryptedAssertion>
</samlp:Response>
</S:Body>
</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'>
Cantor & Josefsson Expires September 3, 2011 [Page 17]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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>
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 September 3, 2011 [Page 18]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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. SASL servers
should be aware that SAML IdPs will track - to some extent - user
access to their services.
It is also out of scope of the mechanism to determine under what
Cantor & Josefsson Expires September 3, 2011 [Page 19]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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 September 3, 2011 [Page 20]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
8. IANA Considerations
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
Cantor & Josefsson Expires September 3, 2011 [Page 21]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
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.
[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.
[SAMLECP20]
Cantor, S., "SAML V2.0 Enhanced Client or Proxy Profile
Version 2.0", OASIS Working Draft OASIS.sstc-saml-ecp-
v2.0-wd02, February 2011.
[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
Cantor & Josefsson Expires September 3, 2011 [Page 22]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
Note soap11, May 2000, <http://www.w3.org/TR/SOAP/>.
9.2. Normative References for GSS-API Implementers
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[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.
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.
Cantor & Josefsson Expires September 3, 2011 [Page 23]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
Appendix A. Acknowledgments
The authors would like to thank Klaas Wierenga, Sam Hartman, and Nico
Williams for their contributions.
Cantor & Josefsson Expires September 3, 2011 [Page 24]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
Appendix B. Changes
This section to be removed prior to publication.
o 01 Updated reference to Version 2.0 of ECP profile and added
initial channel binding material.
o 00 Added GSS-API and GS2 discussions to
draft-cantor-ietf-sasl-saml-ec-00 and renamed as kitten draft.
o draft-cantor-ietf-sasl-saml-ec-00, Initial Revision, largely
adapted from draft-wierenga-ietf-sasl-saml-00.
Cantor & Josefsson Expires September 3, 2011 [Page 25]
Internet-Draft SAML ECP SASL & GSS-API Mechanisms March 2011
Authors' Addresses
Scott Cantor
Internet2
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 September 3, 2011 [Page 26]
Html markup produced by rfcmarkup 1.129c, available from
https://tools.ietf.org/tools/rfcmarkup/