Network Working Group K. Wierenga
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track E. Lear
Expires: August 29, 2011 Cisco Systems GmbH
S. Josefsson
SJD AB
February 25, 2011
A SASL and GSS-API Mechanism for SAML
draft-ietf-kitten-sasl-saml-02.txt
Abstract
Security Assertion Markup Language (SAML) has found its usage on the
Internet for Web Single Sign-On. Simple Authentication and Security
Layer (SASL) and the Generic Security Service Application Program
Interface (GSS-API) are application frameworks to generalize
authentication. This memo specifies a SASL mechanism and a GSS-API
mechanism for SAML 2.0 that allows the integration of existing SAML
Identity Providers with applications using SASL and GSS-API.
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 August 29, 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
Wierenga, et al. Expires August 29, 2011 [Page 1]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
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 Redirect . . . . . . . . . . . . . . . . . . . . . 9
4.4. Client Empty Response and other . . . . . . . . . . . . . 10
4.5. Outcome and parameters . . . . . . . . . . . . . . . . . . 10
5. SAML GSS-API Mechanism Specification . . . . . . . . . . . . . 11
5.1. GSS-API Principal Name Types for SAML . . . . . . . . . . 11
6. Channel Binding . . . . . . . . . . . . . . . . . . . . . . . 12
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. XMPP . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.2. IMAP . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 20
8.1. Man in the middle and Tunneling Attacks . . . . . . . . . 20
8.2. Binding SAML subject identifiers to Authorization
Identities . . . . . . . . . . . . . . . . . . . . . . . . 20
8.3. User Privacy . . . . . . . . . . . . . . . . . . . . . . . 20
8.4. Collusion between RPs . . . . . . . . . . . . . . . . . . 20
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
10.1. Normative References . . . . . . . . . . . . . . . . . . . 22
10.2. Informative References . . . . . . . . . . . . . . . . . . 23
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 24
Appendix B. Changes . . . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
Wierenga, et al. Expires August 29, 2011 [Page 2]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 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.
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
[RFC3501] and XMPP [RFC3920]. The effect is to make modular
authentication, so that newer authentication mechanisms can be added
as needed. This memo specifies just such a mechanism.
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 new 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.
As currently envisioned, this mechanism is to allow the interworking
between SASL and SAML in order to assert identity and other
attributes to relying parties. As such, while servers (as relying
parties) will advertise SASL mechanisms (including SAML), clients
will select the SAML SASL mechanism as their SASL mechanism of
choice.
The SAML mechanism described in this memo aims to re-use the
available SAML deployment to a maximum extent and therefore does not
establish a separate authentication, integrity and confidentiality
mechanism. The mechanisms assumes a security layer, such as
Transport Layer Security (TLS), to protect against some attacks.
Figure 1 describes the interworking between SAML and SASL: this
document requires enhancements to the Relying Party and to the Client
(as the two SASL communication end points) but no changes to the SAML
Identity Provider are necessary. To accomplish this goal some
indirect messaging is tunneled within SASL, and some use of external
methods is made.
Wierenga, et al. Expires August 29, 2011 [Page 3]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
+-----------+
| |
>| Relying |
/ | Party |
// | |
// +-----------+
SAML/ // ^
HTTPs // +--|--+
// | S| |
/ S | A| |
// A | M| |
// S | L| |
// L | | |
// | | |
</ +--|--+
+------------+ v
| | +----------+
| SAML | HTTPs | |
| Identity |<--------------->| Client |
| Provider | | |
+------------+ +----------+
Figure 1: Interworking Architecture
Wierenga, et al. Expires August 29, 2011 [Page 4]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 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 assumed to be familiar with the terms used in the SAML
2.0 specification.
Wierenga, et al. Expires August 29, 2011 [Page 5]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
3. Applicability for non-HTTP Use Cases
While SAML itself is merely a markup language, its common use case
these days is with HTTP. What follows is a typical flow:
1. The browser requests a resource of a Relying Party (RP) (via an
HTTP request).
2. The RP sends an HTTP redirect as described in Section 10.3 of
[RFC2616] to the browser to the Identity Provider (IdP) or an IdP
discovery service with an authentication request that contains
the name of resource being requested, some sort of a cookie and a
return URL,
3. The user authenticates to the IdP and perhaps authorizes the
authentication to the service provider.
4. In its authentication response, the IdP redirects the browser
back to the RP with an authentication assertion (stating that the
IdP vouches that the subject has successfully authenticated),
optionally along with some additional attributes.
5. RP now has sufficient identity information to approve access to
the resource or not, and acts accordingly. The authentication is
concluded.
When considering this flow in the context of SASL, we note that while
the RP and the client both must change their code to implement this
SASL mechanism, the IdP must remain untouched. The RP already has
some sort of session (probably a TCP connection) established with the
client. However, it may be necessary to redirect a SASL client to
another application or handler. This will be discussed below. The
steps are shown from below:
1. The Relying Party or SASL server advertises support for the SASL
SAML20 mechanism to the client
2. The client initiates a SASL authentication with SAML20 and sends
a domain
3. The Relying Party transmits an authentication request encoded
using a Universal Resource Identifier (URI) as described in RFC
3986 [RFC3986] and a redirect to the IdP corresponding to the
domain
4. The SASL client now sends an empty response, as authentication
continues via the normal SAML flow.
Wierenga, et al. Expires August 29, 2011 [Page 6]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
5. At this point the SASL client MUST construct a URL containing the
content received in the previous message from the RP. This URL
is transmitted to the IdP either by the SASL client application
or an appropriate handler, such as a browser.
6. Next the client authenticates to the IdP. The manner in which
the end user is authenticated to the IdP and any policies
surrounding such authentication is out of scope for SAML and
hence for this draft. This step happens out of band from SASL.
7. The IdP will convey information about the success or failure of
the authentication back to the the RP in the form of an
Authentication Statement or failure, using a indirect response
via the client browser or the handler. This step happens out of
band from SASL.
8. The SASL Server sends an appropriate SASL response to the client,
along with an optional list of attributes
Please note: What is described here is the case in which the client
has not previously authenticated. If the client can handle SAML
internally it is possible that the client already holds a valid SAML
authentication token so that the user does not need to be involved in
the process anymore, but that would still be external to SASL.
With all of this in mind, the flow appears as follows:
Wierenga, et al. Expires August 29, 2011 [Page 7]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
SASL Serv. Client IdP
|>-----(1)----->| | Advertisement
| | |
|<-----(2)-----<| | Initiation
| | |
|>-----(3)----->| | Authentication Request
| | |
|<-----(4)-----<| | Empty Response
| | |
| |< - - - - - ->| Client<>IDP
| | | Authentication
| | |
|<- - - - - - - - - - - - - - -| Authentication Statement
| | |
|>-----(6)----->| | SASL completion with
| | | status
| | |
----- = SASL
- - - = HTTP or HTTPs (external to SASL)
Figure 2: Authentication flow
Wierenga, et al. Expires August 29, 2011 [Page 8]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
4. SAML SASL Mechanism Specification
Based on the previous figure, the following operations are performed
with the SAML SASL mechanism.
The mechanism is "client first" as discussed in section 3 of
[RFC4422] which means that the initial server challenge will be empty
if the protocol does not support an initial client response.
4.1. Advertisement
To advertise that a server supports SAML 2.0, during application
session initiation, it displays the name "SAML20" in the list of
supported SASL mechanisms.
4.2. Initiation
A client initiates a "SAML20" authentication with SASL by sending the
GS2 header followed by the authentication identifier. The GS2 header
carries the optional authorization identity.
initial-response = gs2-header Idp-Identifier
IdP-Identifier = domain ; domain name with corresponding IdP
The "gs2-header" is specified in [RFC5801], and it is used as
follows. The "gs2-nonstd-flag" MUST NOT be present. Regarding the
channel binding "gs2-cb-flag" field, see Section 5. The "gs2-
authzid" carries the optional authorization identity. Domain name is
specified in [RFC1035].
4.3. Server Redirect
The SASL Server transmits a URI to the IdP that corresponds to the
domain the user provided, with a SAML authentication request in the
form of a SAML assertion as one of the parameters. Note: The SASL
server may have a static mapping of domain to corresponding IdP or
alternatively a DNS-lookup mechanism could be envisioned, but that is
out-of-scope for this document
redirect-url = URI
As before, URI is specified in [RFC3986].
Wierenga, et al. Expires August 29, 2011 [Page 9]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
4.4. Client Empty Response and other
The SASL client hands the URI it received from the server in the
previous step to either a browser or other appropriate handler to
continue authentication externally while sending an empty response to
the SASL server. The URI is encoded according to Section 3.4 of the
SAML bindings 2.0 specification [OASIS.saml-bindings-2.0-os].
empty-response = ""
4.5. Outcome and parameters
The SAML authentication having completed externally, the SASL server
will transmit the outcome of the authentication exchange as success
or failure.
Wierenga, et al. Expires August 29, 2011 [Page 10]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
5. SAML 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 mechanism is actually 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 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 is 1.3.6.1.4.1.11591.4.8.
SAML20 security contexts always have the mutual_state flag
(GSS_C_MUTUAL_FLAG) set to TRUE. SAML does not support credential
delegation, therefore SAML security contexts alway have the
deleg_state flag (GSS_C_DELEG_FLAG) set to FALSE.
The SAML mechanism does not support per-message tokens or
GSS_Pseudo_random.
Note that the GSS-API mechanism MUST only be used by the client when
a secure channel with server authentication (e.g., TLS) is available.
5.1. GSS-API Principal Name Types for SAML
SAML supports standard generic name syntaxes for acceptors such as
GSS_C_NT_HOSTBASED_SERVICE (see [RFC2743], Section 4.1). SAML
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. The query,
display, and exported name syntaxes for SAML principal names are all
the same. There are no SAML-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.
Wierenga, et al. Expires August 29, 2011 [Page 11]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
6. Channel Binding
The "gs2-cb-flag" MUST use "n" because channel binding data cannot be
integrity protected by the SAML negotiation. FIXME: Transfer channel
binding in SAML assertion?
Wierenga, et al. Expires August 29, 2011 [Page 12]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
7. Examples
7.1. XMPP
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. 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>SAML20</mechanism>
</mechanisms>
</stream:features>
Step 4: Client selects an authentication mechanism and provides the
initial client response containing the BASE64 [RFC4648] encoded gs2-
header and domain:
<auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl' mechanism='SAML20'>
biwsZXhhbXBsZS5vcmc</auth>
The decoded string is: n,,example.org
Wierenga, et al. Expires August 29, 2011 [Page 13]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
Step 5: Server sends a BASE64 encoded challenge to client in the form
of an HTTP Redirect to the SAML IdP corresponding to example.org
(https://saml.example.org) with the SAML Authentication Request as
specified in the redirection url: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The decoded challenge is:
Wierenga, et al. Expires August 29, 2011 [Page 14]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
https://saml.example.org/SAML/Browser?SAMLRequest=PHNhbWxwOk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Where the decoded SAMLRequest looks like:
Wierenga, et al. Expires August 29, 2011 [Page 15]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
<samlp:AuthnRequest xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"
ID="_bec424fa5103428909a30ff1e31168327f79474984" Version="2.0"
IssueInstant="2007-12-10T11:39:34Z" ForceAuthn="false"
IsPassive="false"
ProtocolBinding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST"
AssertionConsumerServiceURL=
"https://xmpp.example.com/SAML/AssertionConsumerService">
<saml:Issuer xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">
https://xmpp.example.com
</saml:Issuer>
<samlp:NameIDPolicy xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"
Format="urn:oasis:names:tc:SAML:2.0:nameid-format:persistent"
SPNameQualifier="xmpp.example.com" AllowCreate="true" />
<samlp:RequestedAuthnContext
xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"
Comparison="exact">
<saml:AuthnContextClassRef
xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">
urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport
</saml:AuthnContextClassRef>
</samlp:RequestedAuthnContext>
</samlp:AuthnRequest>
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 sends a BASE64 encoded empty response to the
challenge:
<response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
=
</response>
[ The client now sends the URL to a browser for processing. The
browser engages in a normal SAML authentication flow (external to
SASL), like redirection to the Identity Provider
(https://saml.example.org), the user logs into
https://saml.example.org, and agrees to authenticate to
xmpp.example.com. A redirect is passed back to the client browser
Wierenga, et al. Expires August 29, 2011 [Page 16]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
who sends the AuthN response to the server, containing the subject-
identifier as an attribute. If the AuthN response doesn't contain
the JID, the server maps the subject-identifier received from the IdP
to a JID]
Step 7: Server informs client of successful authentication:
<success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Step 7 (alt): Server informs client of failed authentication:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<temporary-auth-failure/>
</failure>
</stream:stream>
Step 8: 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 9: 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 10: Client binds a resource:
<iq type='set' id='bind_1'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<resource>someresource</resource>
</bind>
Wierenga, et al. Expires August 29, 2011 [Page 17]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
</iq>
Step 11: 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.
7.2. IMAP
The following describes an IMAP exchange. Lines beginning with 'S:'
indicate data sent by the server, and lines starting with 'C:'
indicate data sent by the client. Long lines are wrapped for
readability.
Wierenga, et al. Expires August 29, 2011 [Page 18]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
S: * OK IMAP4rev1
C: . CAPABILITY
S: * CAPABILITY IMAP4rev1 STARTTLS
S: . OK CAPABILITY Completed
C: . STARTTLS
S: . OK Begin TLS negotiation now
C: . CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=SAML20
S: . OK CAPABILITY Completed
C: . AUTHENTICATE SAML20
S: +
C: biwsZXhhbXBsZS5vcmc
S: + aHR0cHM6Ly9zYW1sLmV4YW1wbGUub3JnL1NBTUwvQnJvd3Nlcj9TQU1MUmVx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C:
S: . OK Success (tls protection)
Wierenga, et al. Expires August 29, 2011 [Page 19]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
8. 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.
8.1. Man in the middle and Tunneling Attacks
This mechanism is vulnerable to man in the middle and tunneling
attacks unless a client always verify the server identity before
proceeding with authentication. Typically TLS is used to provide a
secure channel with server authentication.
8.2. Binding SAML subject identifiers to Authorization Identities
As specified in [RFC4422], the server is responsible for binding
credentials to a specific authorization identity. It is therefore
necessary that only specific trusted IdPs be allowed. This is
typical part of SAML trust establishment between RP's and IdP.
8.3. 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 visits, but there is nothing that prohibits
the collection of information. SASL servers should be aware that
SAML IdPs will track - to some extent - user access to their
services.
8.4. Collusion between RPs
It is possible for RPs to link data that they have collected on you.
By using the same identifier to log into every RP, collusion between
RPs is possible. In SAML, targeted identity was introduced.
Targeted identity allows the IdP to transform the identifier the user
typed in to an opaque identifier. This way the RP would never see
the actual user identifier, but a randomly generated identifier.
This is an option the user has to understand and decide to use if the
IdP is supporting it.
Wierenga, et al. Expires August 29, 2011 [Page 20]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
9. IANA Considerations
The IANA is requested to register the following SASL profile:
SASL mechanism profile: SAML20
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
Wierenga, et al. Expires August 29, 2011 [Page 21]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
10. References
10.1. 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.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[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.
[RFC5801] Josefsson, S. and N. Williams, "Using Generic Security
Service Application Program Interface (GSS-API) Mechanisms
in Simple Authentication and Security Layer (SASL): The
Wierenga, et al. Expires August 29, 2011 [Page 22]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
GS2 Mechanism Family", RFC 5801, July 2010.
10.2. Informative References
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
[RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004.
Wierenga, et al. Expires August 29, 2011 [Page 23]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
Appendix A. Acknowledgments
The authors would like to thank Scott Cantor, Joe Hildebrand, Josh
Howlett, Leif Johansson, Diego Lopez, Hank Mauldin, RL 'Bob' Morgan,
Stefan Plug and Hannes Tschofenig for their review and contributions.
Wierenga, et al. Expires August 29, 2011 [Page 24]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
Appendix B. Changes
This section to be removed prior to publication.
o 02 Changed IdP URI to domain per Joe Hildebrand, fixed some typos
o 00 WG -00 draft. Updates GSS-API section, some fixes per Scott
Cantor
o 01 Added authorization identity, added GSS-API specifics, added
client supplied IdP
o 00 Initial Revision.
Wierenga, et al. Expires August 29, 2011 [Page 25]
Internet-Draft A SASL & GSS-API Mechanism for SAML February 2011
Authors' Addresses
Klaas Wierenga
Cisco Systems, Inc.
Haarlerbergweg 13-19
Amsterdam, Noord-Holland 1101 CH
Netherlands
Phone: +31 20 357 1752
Email: klaas@cisco.com
Eliot Lear
Cisco Systems GmbH
Richtistrasse 7
Wallisellen, ZH CH-8304
Switzerland
Phone: +41 44 878 9200
Email: lear@cisco.com
Simon Josefsson
SJD AB
Hagagatan 24
Stockholm 113 47
SE
Email: simon@josefsson.org
URI: http://josefsson.org/
Wierenga, et al. Expires August 29, 2011 [Page 26]
