saml an xml based security assertion markup language
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Introduction
XML standard for exchanging authentication and authorization data between security domains, i.e. identity provider and service provider.
Solve the single sign-on (SSO) problem at intranet level using cookies.
SAML assumes principal (user) is enrolled at least with one identity provider.
Why is SAML required ?
Limitations of Browser cookiesCross-Domain SSO (CDSSO) problem
SSO Interoperability
SSO and CDSSO are completely proprietary Web Services
Authentication/integrity services on an end-to-end basis Federation
identity management across organizational boundaries to a
single (or at least a reduced set) Federated Identity
SAML Use Cases
There are 3 use cases in SAML:
- Single sign-on (SSO)
- Authorization service
- Back office transaction
Each use case have one or more scenarios
that provide a more detailed roadmap of interaction
SAML Overview
Specification for exchanging authentication and authorization information using XML-based security
- XML schema and definition for security assertions- XML schema and definition for a request/response protocol- Rules on using assertions with standard transport and messaging frameworks. Bindings and Profiles
Emerging OASIS standard involving Vendors and Users Codifies current system outputs rather than inventing new
technology
SAML Assertions
Declaration of facts (statements) about a subject
Contains multiple assertion statements Can be digitally signed 3 kinds of assertion statements related to
security:1. Authentication2. Attribute3. Authorization Decision
Common Information in all Assertions
Issuer and issuance timestamp Assertion ID Subject
Name and security domain Optional subject confirmation like public key
Conditions under which assertion is valid Special conditions like – assertion validity period, audience
restriction and target restriction SAML clients must reject assertions containing
unsupported conditions.
Authentication AssertionThe Issuing authority asserts that subject S, was authenticated by means M, at time T.
Attribute Assertion
The Issuing authority asserts that subject S, isassociated with attributes A, B,…, with values a, b, c.
Authorization Decision Assertion
The Issuing authority decides whether to grant the
request by subject S, for access type A, to resource R
Assertions - continued
Assertions without the rest of the structure may be provided for existing tightly coupled environments who may need their own protocol.
SAML is fully beneficial when parties with no direct knowledge of each other can interact via a third-party introduction
SAML Protocol simple request-response protocol
<samlp:Request xmlns:samlp="urn:oasis:names:tc:SAML:1.0:protocol" MajorVersion="1" MinorVersion="1“RequestID="..." IssueInstant="..."><!-- insert other SAML elements here --> </samlp:Request>
<samlp:Response xmlns:samlp="urn:oasis:names:tc:SAML:1.0:protocol" MajorVersion="1" MinorVersion="1“ResponseID="...“InResponseTo="..." IssueInstant="..."><!-- insert other SAML elements here, including assertions --> </samlp:Response>
Authentication Assertion Request
What are the authentication assertions which are available for this subject
Successful responses are in the form of assertions containing an authentication statement
It is assumed that the requester and responder have a trust relationship and are talking about the same subject
Attribute Assertion Request
The requested attribute is returned for this subject
Response is in the form of an assertion containing attribute statement
Requester can be denied access to some of the attributes and allowed access to a partial list of attributes
Authorization Decision Assertion Request
Given the evidence is this subject allowed access to the specified resource in the specified manner with the given evidence?
Response is in the form of an assertion containing an authorization decision statement
Protocol Binding and Profile
Binding – mapping of SAML request/response message exchanges into standard communication protocols. SOAP-over-HTTP binding is the baseline
Profile – describes how SAML assertions are embedded into and extracted from a framework or protocol. Web browser profile for SSO SOAP profile for securing SOAP payloads
SOAP Profile
SAML is used to
provide assertions
about a resource in
the SOAP Body of
the same document
Web Brower Profiles
Assumptions
Standard commercial browser and HTTP(S) User authenticated to local source site Assertion’s subject refers to the user
What happens when user tries to access target site
Tiny authentication assertion reference travels with request so real assertion can be de-referenced
POST of real assertion can occur
SSO Pull Scenario Using Web Browser - explained Step 1 : Access inter-site transfer URL:
User authenticated with http://Company.com Clicks on a link that looks like it will take the user to
http://Travel.com/reserve_hotel.cgi It really takes the user to inter-site transfer URL:https://Company.com/intersite?Target=Travel.com/reserve_hotel.cgi
Step 2 : Redirect with artifact: Reference to user’s authentication assertion generated as SAML
“artifact” (8-byte base64 string) User redirected to assertion consumer URL, with artifact and
target attached:https://Travel.com?Target=Travel.com/
reserve_hotel.cgi&SAMLart=<artifact>
References
http://www.computerworld.com/developmenttopics/development/webdev/story/0,10801,73712,00.html
http://www.simc-inc.org/archive0002/February02/devwed1015_rouault.pdf
http://en.wikipedia.org/wiki/SAML http://xml.coverpages.org/saml.html http://xml.coverpages.org/SAML-TechOverviewV20-Draft
7874.pdf