One document matched: draft-ietf-kitten-sasl-saml-ec-00.xml
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<rfc ipr="trust200902" docName="draft-ietf-kitten-sasl-saml-ec-00.txt"
category="std">
<front>
<title abbrev="SAML ECP SASL & GSS-API Mechanisms">
SAML Enhanced Client SASL and GSS-API Mechanisms
</title>
<author fullname="Scott Cantor" initials="S." surname="Cantor">
<organization>Internet2</organization>
<address>
<postal>
<street>2740 Airport Drive</street>
<city>Columbus</city>
<code>43219</code>
<region>Ohio</region>
<country>United States</country>
</postal>
<phone>+1 614 247 6147</phone>
<email>cantor.2@osu.edu</email>
</address>
</author>
<author initials="S." surname="Josefsson" fullname="Simon Josefsson">
<organization>SJD AB</organization>
<address>
<postal>
<street>Hagagatan 24</street>
<city>Stockholm</city>
<code>113 47</code>
<country>SE</country>
</postal>
<email>simon@josefsson.org</email>
<uri>http://josefsson.org/</uri>
</address>
</author>
<date year="2011"/>
<abstract>
<t>
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.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
<xref target="OASIS.saml-core-2.0-os">Security Assertion Markup
Language (SAML) 2.0</xref> 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 <xref target="OASIS.saml-bindings-2.0-os">bindings</xref>,
and <xref target="OASIS.saml-profiles-2.0-os">interoperability profiles</xref>
designed for different use cases. Additional profiles and extensions
are also routinely developed and published.
</t>
<t>
<xref target="RFC4422">Simple Authentication and Security Layer
(SASL)</xref> 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 <xref target="RFC3920">XMPP</xref>. The
effect is to make authentication modular, so that newer authentication
mechanisms can be added as needed.
</t>
<t>
The <xref target="RFC2743">Generic Security Service Application
Program Interface (GSS-API)</xref> 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 <xref target="RFC5801">GS2</xref>. 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.
</t>
<t>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.
</t>
<t>The SAML mechanism described in this document is an adaptation of an
existing SAML profile, the <xref target="SAMLECP20">Enhanced Client or
Proxy (ECP) Profile (V2.0)</xref>, and therefore does not establish
a separate authentication, integrity and confidentiality mechanism.
It is anticipated that existing security layers, such as Transport Layer
Security (TLS), will continued to be used.</t>
<t><xref target="overview"/> 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.</t>
<t> <figure anchor="overview" title="Interworking
Architecture"> <artwork><![CDATA[
+-----------+
| SAML |
| Relying |
| Party |
| |
+-----------+
^
+--|--+
| S| |
S | A| |
A | M| |
S | L| |
L | | |
| | |
+--|--+
+------------+ v
| | +----------+
| SAML | SAML SOAP | |
| Identity |<--------------->| Client |
| Provider | Binding | |
+------------+ +----------+
]]></artwork> </figure> </t>
</section>
<section anchor="terminology" title="Terminology">
<t>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 <xref target="RFC2119"/>.</t>
<t>The reader is also assumed to be familiar with the terms used in the SAML
2.0 specification, and an understanding of the
<xref target="SAMLECP20">Enhanced Client or Proxy (ECP) Profile (V2.0)</xref>
is necessary, as part of this mechanism explicitly reuses and references it.</t>
<t>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.</t>
</section>
<section title="Applicability for Non-HTTP Use Cases">
<t>While SAML is designed to support a variety of application scenarios,
the profiles for authentication defined in the original standard are
designed around <xref target="RFC2616">HTTP</xref> 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
<xref target="SAMLECP20">Enhanced Client or Proxy (ECP) Profile (V2.0)</xref>,
as applied to the web/HTTP service use case:</t>
<t>
<list style="numbers">
<t>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.</t>
<t>The RP, desiring SAML authentication and noting the client's capabilities,
responds not with an HTTP redirect or form, but with a
<xref target="W3C.soap11">SOAP</xref> 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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
</list>
</t>
<t>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 <xref target="RFC4422">SASL</xref>, this mechanism is
"client-first" for consistency with GS2. The steps are shown below:</t>
<t>
<list style="numbers">
<t>The server MAY advertise the SAML20EC and/or SAML20EC-PLUS mechanisms.</t>
<t>The client initiates a SASL authentication with SAML20EC or SAML20EC-PLUS.</t>
<t>The server sends the client a challenge consisting of a SOAP envelope containing
its SAML <AuthnRequest>.</t>
<t>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.</t>
<t>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.</t>
<t> The SASL Server indicates success or failure.</t>
</list>
</t>
<t>Note: The details of the SAML processing, which are consistent with the
<xref target="SAMLECP20">Enhanced Client or Proxy (ECP) Profile (V2.0)</xref>,
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.</t>
<t>
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.</t>
<t> With all of this in mind, the typical flow appears as follows:</t>
<t>
<figure anchor="flow" title="Authentication flow">
<artwork><![CDATA[
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)
]]>
</artwork>
</figure></t>
</section>
<section title="SAML SASL Mechanism Specification"> <t>Based on the
previous figures, the following operations are defined by the SAML
SASL mechanism:</t>
<section title="Advertisement" anchor="advertisement"> <t>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).</t>
</section>
<section title="Initiation" anchor="initiation">
<t>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).</t>
<t>The format of the initial client response is as follows:</t>
<figure>
<artwork>
holder-of-key = "urn:oasis:names:tc:SAML:2.0:cm:holder-of-key"
initial-response = gs2-cb-flag "," [gs2-authzid] "," [holder-of-key]
</artwork>
</figure>
<t>The gs2-cb-flag MUST be set as defined in <xref target="RFC5801"/>
to indicate whether the client supports channel binding. This takes
the place of the PAOS HTTP header extension used in <xref target="SAMLECP20"/>
to indicate channel binding support.</t>
<t>The optional "gs2-authzid" field holds the authorization identity,
as requested by the client.</t>
<t>The optional "holder-of-key" 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
<xref target="SAMLECP20"/> to indicate "holder of key" support.</t>
</section>
<section title="Server Response" anchor="serverresponse">
<t>The SASL server responds with a SOAP envelope constructed in
accordance with section 2.3.2 of <xref target="SAMLECP20"/>. This
includes adhering to the SOAP header requirements of the
<xref target="OASIS.saml-bindings-2.0-os">SAML PAOS Binding</xref>,
for compatibility with the existing profile. Various SOAP headers
are also consumed by the client in exactly the same manner prescribed
by that section.</t>
</section>
<section title="User Authentication with Identity Provider" anchor="userauthn">
<t>Upon receipt of the <xref target="serverresponse">Server
Response</xref>, the steps described in sections 2.3.3 through
2.3.6 of <xref target="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.</t>
<t>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 <xref target="RFC2617"/> and
TLS client authentication as defined in <xref target="RFC5246"/>.</t>
</section>
<section title="Client Response" anchor="clientresponse">
<t>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 <xref target="SAMLECP20"/>. This includes adhering to
the SOAP header requirements of the <xref target="OASIS.saml-bindings-2.0-os">SAML
PAOS Binding</xref>, 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.</t>
</section>
<section title="Outcome" anchor="outcome">
<t>The SAML protocol exchange having completed, the SASL server will
transmit the outcome to the client depending on local validation of
the client responses.</t>
</section>
<section title="Additional Notes" anchor="notes">
<t>Because this mechanism is an adaptation of an HTTP-based profile,
there are a few requirements outlined in <xref target="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.</t>
<t>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 the responseConsumerURL and AssertionConsumerServiceURL attributes
with its service name, expressed as an absolute URI. The parties then
perform the steps described in <xref target="SAMLECP20"/> as usual.</t>
</section>
</section>
<section title="SAML EC GSS-API Mechanism Specification">
<t>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.</t>
<t>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).</t>
<t>The GSS-API mechanism OID for SAML EC is 1.3.6.1.4.1.11591.4.6.</t>
<t>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.</t>
<t>The mutual authentication property of this mechanism relies on
successfully comparing the TLS server identity with the negotiated
target name. Since the TLS channel is managed by the application
outside of the GSS-API mechanism, the mechanism itself is unable to
confirm the name while the application is able to perform this
comparison for the mechanism. For this reason, applications MUST
match the TLS server identity with the target name, as discussed in
<xref target="RFC6125"/>.</t>
<t>The SAML EC mechanism does not support per-message tokens or
GSS_Pseudo_random.</t>
<section title="GSS-API Principal Name Types for SAML EC">
<t>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 <xref target="OASIS.saml-metadata-2.0-os">SAML metadata</xref>.</t>
<t>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.</t>
<t>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.</t>
<t>GSS-API name attributes may be defined in the future to hold the
normalized SAML EC Identifier.</t>
</section>
</section>
<section title="Example">
<t>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:</t>
<t>Step 1: Client initiates stream to server:</t>
<figure><artwork>
<![CDATA[
<stream:stream xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='example.com' version='1.0'>
]]>
</artwork></figure>
<t>Step 2: Server responds with a stream tag sent to client:</t>
<figure><artwork>
<![CDATA[
<stream:stream
xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams'
id='some_id' from='example.com' version='1.0'>
]]>
</artwork></figure>
<t>Step 3: Server informs client of available authentication
mechanisms:</t>
<figure><artwork>
<![CDATA[
<stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
<mechanism>SAML20EC</mechanism>
</mechanisms>
</stream:features>
]]>
</artwork></figure>
<t>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):</t>
<figure><artwork>
<![CDATA[
<auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl' mechanism='SAML20EC'>
biws
</auth>
]]>
</artwork></figure>
<t>The initial response is "n,," which signals that channel binding
is not used, there is no authorization identity, and the client does
not support key-based confirmation.</t>
<t>Step 5: Server sends a challenge to client in the form of a SOAP
envelope containing its SAML <AuthnRequest>:</t>
<figure><artwork>
<![CDATA[
<challenge xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
PFM6RW52ZWxvcGUNCiAgICB4bWxuczpzYW1sPSJ1cm46b2FzaXM6bmFtZXM6dGM6U0FNTDoy
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CiAgICAgIDxzYW1sOklzc3VlciB4bWxuczpzYW1sPSJ1cm46b2FzaXM6bmFtZXM6dGM6U0FN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</challenge>
]]>
</artwork></figure>
<t>The <xref target="RFC4648">Base64</xref> decoded envelope:</t>
<figure><artwork>
<![CDATA[
<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>
]]>
</artwork></figure>
<t>Step 5 (alt): Server returns error to client:</t>
<figure> <artwork>
<![CDATA[
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<incorrect-encoding/>
</failure>
</stream:stream>
]]>
</artwork></figure>
<t>Step 6: Client relays the request to IdP in a SOAP message
transmitted over HTTP (over TLS). HTTP portion not shown, use of
Basic Authentication is assumed. The body of the SOAP envelope is
exactly the same as received in the previous step.</t>
<figure><artwork>
<![CDATA[
<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>
]]>
</artwork></figure>
<t>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).</t>
<figure><artwork>
<![CDATA[
<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>
]]>
</artwork></figure>
<t>Step 8: Client sends SOAP envelope containing the SAML
<Response> as a response to the SASL server's challenge:</t>
<figure><artwork>
<![CDATA[
<response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>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</response>
]]>
</artwork></figure>
<t>The <xref target="RFC4648">Base64</xref> decoded envelope:</t>
<figure><artwork>
<![CDATA[
<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>
]]>
</artwork></figure>
<t>Step 9: Server informs client of successful authentication:</t>
<figure><artwork>
<![CDATA[
<success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
]]>
</artwork></figure>
<t>Step 9 (alt): Server informs client of failed authentication:</t>
<figure><artwork>
<![CDATA[
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<temporary-auth-failure/>
</failure>
</stream:stream>
]]>
</artwork></figure>
<t>Step 10: Client initiates a new stream to server:</t>
<figure><artwork>
<![CDATA[
<stream:stream xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='example.com' version='1.0'>
]]>
</artwork></figure>
<t>Step 11: Server responds by sending a stream header to client along
with any additional features (or an empty features element):</t>
<figure><artwork>
<![CDATA[
<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>
]]>
</artwork></figure>
<t>Step 12: Client binds a resource:</t>
<figure><artwork>
<![CDATA[
<iq type='set' id='bind_1'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<resource>someresource</resource>
</bind>
</iq>
]]>
</artwork></figure>
<t>Step 13: Server informs client of successful resource binding:</t>
<figure><artwork>
<![CDATA[
<iq type='result' id='bind_1'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<jid>somenode@example.com/someresource</jid>
</bind>
</iq>
]]>
</artwork></figure>
<t>Please note: line breaks were added to the base64 for clarity.</t>
</section>
<section title="Security Considerations">
<t>
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.
</t>
<t>
Version 2.0 of the <xref target="SAMLECP20">Enhanced Client or Proxy
Profile</xref> 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.
</t>
<section title="Risks Left Unaddressed">
<t>
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.
</t>
<t>
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.
</t>
</section>
<section title="User Privacy">
<t>
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.
</t>
<t>
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.
</t>
</section>
<section title="Collusion between RPs">
<t>
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.
</t>
</section>
</section>
<section title="IANA Considerations">
<t>The IANA is requested to register the following SASL profile:</t>
<t/>
<t>SASL mechanism profiles: SAML20EC and SAML20EC-PLUS</t>
<t>Security Considerations: See this document</t>
<t>Published Specification: See this document</t>
<t>For further information: Contact the authors of this document.</t>
<t>Owner/Change controller: the IETF</t>
<t>Note: None</t>
</section>
</middle>
<back>
<references title="Normative References">
&RFC2119;
&RFC2617;
&RFC4422;
&RFC4648;
&RFC5246;
&RFC6125;
&SAML20;
&SAML20BIND;
&SAML20PROF;
&SOAP;
<reference anchor="SAMLECP20">
<front>
<title>SAML V2.0 Enhanced Client or Proxy Profile Version 2.0</title>
<author initials="S." surname="Cantor" fullname="Scott Cantor">
<organization>Internet2</organization>
</author>
<date month="August" year="2011" />
</front>
<seriesInfo name="OASIS Working Draft" value="OASIS.sstc-saml-ecp-v2.0-wd04" />
<format type="PDF" target="http://www.oasis-open.org/committees/download.php/43310/sstc-saml-ecp-v2.0-wd04.pdf"/>
</reference>
</references>
<references title="Normative References for GSS-API Implementers">
&RFC2743;
&RFC5801;
</references>
<references title="Informative References">
&RFC2616;
&RFC3920;
&SAML20META;
</references>
<section title="Acknowledgments">
<t>
The authors would like to thank Klaas Wierenga, Sam Hartman, and
Nico Williams for their contributions.
</t>
</section>
<section title="Changes"> <t>This section to be removed
prior to publication.</t> <t> <list style="symbols">
<t>draft-ietf-kitten-sasl-saml-ec-00, Initial
Revision, first WG-adopted draft. Removed support for unsolicited SAML responses.</t> </list> </t>
</section>
</back>
</rfc>
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