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Introduction to Windows Azure Active Directory Federation Part 1

by Steve Syfuhs / November 30, 2012 12:19 AM

Earlier this week Microsoft released some interesting numbers regarding Windows Azure Active Directory (WAAD) authentication.

Since the inception of the authentication service on the Windows Azure platform in 2010, we have now processed 200 BILLION authentications for 50 MILLION active user accounts. In an average week we receive 4.7 BILLION authentication requests for users in over 420 THOUSAND different domains.

[…] To put it into perspective, in the 2 minutes it takes to brew yourself a single cup of coffee, Windows Azure Active Directory (AD) has already processed just over 1 MILLION authentications from many different devices and users around the world.  Not only are we processing a huge number of authentications but we’re doing it really fast!  We respond to 9,000 requests per second and in the U.S. the average authentication takes less than 0.7 seconds.

Whoa.

Now, some people may be wondering what this is all about. Where are all these requests coming from? What domains? Who? Huh? What? It’s actually pretty straightforward: 99.99999999% of all these requests are coming from Office 365 and Dynamics CRM.

Windows Azure Active Directory started as the authentication service for Office 365. The service is built on the Microsoft Federation Gateway, which is the foundation for Windows Live/Microsoft accounts. As the platform matured Microsoft opened the system to allow more applications to authenticate against the service. It has since transitioned into it’s proper name Windows Azure Active Directory.

The system at it’s core is simply a multitenant directory of users. Each tenant is tied to at least one unique domain. Each tenant can then allow applications to federate. This is basically how Office 365 works. When you create a new Office 365 account, the provisioning system creates a new tenant in WAAD and ties it to a subdomain of onmicrosoft.com, so you would for instance get contoso.onmicrosoft.com. Once the tenant is created the provisioning system then goes off to the various services you’ve selected like Exchange, SharePoint, CRM, etc and starts telling them to create their various things necessary for service. These services now know about your WAAD tenant.

This is all well and good, but you’re now using contoso.onmicrosoft.com, and you would rather use a different domain like contoso.com for email and usernames. Adding a domain to Office 365 requires telling both WAAD and the various services that a new domain is available to use in the tenant. Now WAAD has two domains associated with it.

Now we can create users with our custom domain contoso.com, but there’s like a thousand users and you have Active Directory locally. It would be much better if we could just log into Office 365 using our own Active Directory credentials, and it would be so much nicer on the administrator if he didn’t have to create a thousand users. This calls for federation between WAAD and AD through Active Directory Federation Services (too. many. AD-based. names!).

Things get a little more complicated here. Before looking at federation between WAAD and AD we should take a look at how authentication normally works in Office 365.

First a user will try to access an application like SharePoint. SharePoint doesn’t see a session for the user so it redirects the user to login.microsoftonline.com, which is the public face of Windows Azure Active Directory. The user enters their credentials managed through your WAAD tenant, and is then redirected back to SharePoint with a token. SharePoint consumes the token and creates a session for the user. This is a standard process called passive federation. The federation is between SharePoint and WAAD. SharePoint and the various other services trust login.microsoftonline.com (and only login.microsoftonline.com) to issue tokens, so when a user has a token issued by login.microsoftonline.com its understood that the user has been authenticated and is now trusted. Clear as mud, right?

Allowing authentication via your on premise Active Directory complicates things a little. This involves creating a trust between Windows Azure Active Directory and your Active Directory through a service called Active Directory Federation Services. A trust is basically a contract that states WAAD will understand and allow tokens received from ADFS. With this trust in place, any authentication requests to WAAD through login.microsoftonline.com will be passed to your ADFS server. Once your ADFS server authenticates you, a token is generated and sent back to login.microsoftonline.com. This token is then consumed, and a new token is generated by login.microsoftonline.com and issued to whichever service asked for you to log in. Remember what I said above: Office 365 services only trust tokens issued by login.microsoftonline.com. Everything flows through WAAD.

That was a pretty high-level discussion of how things work, but unfortunately it’s missing a few key pieces like DirSync. In my next post I’ll dive much deeper into the inner workings of all these bits and pieces explaining how Windows Azure Active Directory federates with your on premise Active Directory.

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Steve is a renaissance kid when it comes to technology. He spends his time in the security stack.