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ADFS2 is not always SAML 2.0 standards compliant

Now the madness with ADFS2 SAML assertions via WS-Trust 1.3 – and how they are not valid for use with Amazon Web Services (AWS).

lexx:saml$ aws sts assume-role-with-saml --role-arn $role --principal-arn $principal --saml-assertion $assertion
A client error (InvalidIdentityToken) occurred when calling the AssumeRoleWithSAML operation: Responses must contain SubjectConfirmatonData with a Recipient and NotOnOrAfter

This failed due to a missing Recipient attribute on the SubjectConfirmationData element. Of course; I can’t modify the assertion to add the missing Recipient; as the SAML token is signed:

lexx:saml$ aws sts assume-role-with-saml --role-arn $role --principal-arn $principal --saml-assertion $assertion
A client error (InvalidIdentityToken) occurred when calling the AssumeRoleWithSAML operation: Response signature invalid

Second fail is because I’ve modified the assertion to add the missing attribute; but now the signature is invalid.

When you get an assertion from the ADFS Identity Provider via the IdP Web Landing Page, for AWS, the assertion includes a “recipient”:

<subjectconfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">
  <subjectconfirmationdata NotOnOrAfter="2015-02-08T22:48:18.520Z" Recipient="https://signin.aws.amazon.com/saml"></subjectconfirmationdata>
</subjectconfirmation>

When you ask for an assertion from the WS-Trust 1.3 endpoint; it is missing:

<subjectconfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">
  <subjectconfirmationdata NotOnOrAfter="2015-02-09T05:03:10.517Z"></subjectconfirmationdata>
</subjectconfirmation>

Seems to be a common problem with ADFS2 whereby ADFS1 did it correctly. It’s not just me

In the original SAML 2.0 Core spec – Line 725 – Recipient is an optional attribute in the SubjectConfirmationData element. However in subsequent errata for the specification, Errata 02 in May 2007, made it mandatory. Errata 05 still includes this requirement.

At lease one bearer element MUST contain a element that itself MUST contain a Recipient attribute containing the service provider’s assertion consumer service URL

Of course; Amazon adhere to the Standard:

The value of the Recipient attribute inside the SubjectConfirmationData element must match the AWS endpoint (https://signin.aws.amazon.com/saml)

It seems that ADFS2 doesn’t provide valid SAML 2.0 assertions issued via the WS-Trust 1.3 endpoint. Since this has been a standard since for almost 8 years, how does ADFS2 even claim to be standards based.

SAML assertion from ADFS2 via SOAP endpoint

According to Wikipedia, Microsoft Active Directory Federation Services (ADFS) is:

… a software component developed by Microsoft that can be installed on Windows Server operating systems to provide users with single sign-on access to systems and applications located across organizational boundaries. It uses a claims-based access control authorization model to maintain application security and implement federated identity.

ADFS can provide Single sign as an identity provider to users, but what if a developer needs the same sign on outside of “browser land”? One option is to scrape webpage responses, but a better option is receiving a SAML Assertion using SOAP endpoints exposed via Microsoft ADFS, as long as they are enabled. You can use SOAP 1.2 with WS-A Addressing and mixed message security with the username/password in the SOAP headers secured over HTTPS, and get a valid SAML assertion.

There is Mex Endpoint (Anonymous by default) provided by ADFS2 or greater (if not disabled) at
https://youradfsserver.com.au/adfs/services/trust/mex
If you want to play with SOAP based claim requests, use a tool like SoapUI and consume the Mex endpoint as the WSDL. You can then construct Soap messages, and see if you get a valid response – which would contain an assertion.

The SOAP Endpoint for requesting a SAML token using WS-Trust 1.3 and mixed security would be
https://youradfsserver.com.au/adfs/services/trust/13/usernamemixed

The client credentials are included in the header of a SOAP message. Confidentiality is preserved at the transport layer (SSL/TLS); hence a usernamemixed endpoint.

Here is an example SOAP request for usernamemixed:

You can also use curl to post the soap request as shown:

Given all that; this actually won’t work for AWS; given ADFS2 actually breaks the SAML2.0 standards updated in 2012. Next post will detail this.