Keeping AD FS Integrated Windows Authentication (IWA/WIA) Clients Signed In

Over the last couple of years we’ve started doing less AD FS work, with the advent of Password Hash Sync for Azure AD sign-on, and Microsoft’s continued investment in Azure AD Premium. We’ve also seen a few organisations struggle to operate AD FS successfully, even if I personally like the technology. So I’ve changed our approach to unveil all of this with as much realism as possible, and to draw some feature comparisons in both directions. We also spend a lot of time talking about expectations of SSO, and how the ways we think about SSO on the web aren’t quite as automatic as what we get with Windows hashes and tickets.

So… what this means is that we don’t do as much AD FS work anymore, and when Microsoft released a hotfix for AD FS in the August 2014 update rollup, it didn’t catch my eye. This hotfix and the related configuration that needs to be added to the AD FS trust with Azure AD are documented in the newer Configure Persistent Single Sign-On article, and I first picked up on this configuration in the Azure MFA article for AD FS. At any rate, this configuration specifies two new Issuance Transformation Claims Rules for the AD FS Relying Party Trust with Azure AD (AKA “Microsoft Office 365 Identity Platform”):

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Coordinating AD FS 2012 R2 token lifetimes to reduce logon prompts, enforce revocation and limit session duration over public networks

Back in February, I posted a question on the Geneva forum about Adjusting token lifetimes at the Web Application Proxy (WAP) for external access:

Does the Web Application Proxy or AD FS have any separate controls for adjusting token lifetimes to a different value via WAP than directly at AD FS? I can see there’s a session cookie for EdgeAccessCookie that WAP issues but this seems to be entirely undocumented at present. I’ve poked around in C:\Windows\ADFS\Config\microsoft.identityServer.proxyservice.exe.config (also undocumented as far as I can tell) but I’m not finding anything there either. We used to have some of these controls (sort of) with TMG/UAG. Are they totally gone now? With the AD FS Proxy this was less of an issue because it was only publishing AD FS but this is something that I’d hope to be able to control with a Reverse Proxy. Any ideas?

I didn’t get any replies, but after carrying out some tests of my own, I noticed the EdgeAccessCookie, and found a bit of information on TechNet:

After the user is authenticated, the AD FS server issues a security token, the ‘edge token’, containing the following information and redirects the HTTPS request back to the Web Application Proxy server:

  • The resource identifier that the user attempted to access.
  • The user’s identity as a user principal name (UPN).
  • The expiry of the access grant approval; that is, the user is granted access for a limited period of time, after which they are required to authenticate again.
  • Signature of the information in the edge token.

Web Application Proxy receives the redirected HTTPS request from the AD FS server with the edge token and validates and uses the token as follows:

  • Validates that the edge token signature is from the federation service that is configured in the Web Application Proxy configuration.
  • Validates that the token was issued for the correct application.
  • Validates that the token has not expired.
  • Uses the user identity when required; for example to obtain a Kerberos ticket if the backend server is configured to use Integrated Windows authentication.

If the edge token is valid, Web Application Proxy forwards the HTTPS request to the published web application using either HTTP or HTTPS.

This quickly became one of those things where there was insufficient documentation and limited project time, so I had to put this inquiry on hold. Then in July, I posted a question on the Application Proxy blog (a great resource), to see if this is something that they planned to document. The response that I got from Ian Parramore was unexpected and pleasing:

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Office 365 Single Sign Out with ISA or TMG as the ADFS Proxy

Over the last year I’ve spent a decent chunk of my time shaping and delivering Identity and Access Management workshops for Office 365 projects at Content and Code. This is generally underpinned by Active Directory Federation Services v2.0 (ADFS). In fact I don’t think we’ve done a single Office 365 project without it. Along the way I’ve become acquainted with many of the nuances of the sign on and sign out experiences as they differ across Office 365 services, client applications and different (valid) network perimeter technologies. In this post I will mainly focus on the security implications of publishing ADFS through ISA or TMG Reverse Proxies in the place of ADFS Proxy servers. In the majority of our engagements we’ve considered this option (potentially allowing our clients to consolidate infrastructure) since ISA, TMG or similar Reverse Proxies are commonly deployed. Yet we need to evaluate with full awareness of how ADFS operates without a Claims-aware Reverse Proxy such as the ADFS Proxy. This gets pretty technical, so I’m assuming some high-level familiarity with ADFS, Reverse Proxies and Office 365.


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