Deep dive into AD FS and MS WAP – Overview

Hi everyone,

If you’ve followed my blog at all, you will notice I spend a fair amount of my time writing about the products and technologies powering the integration of on-premises and cloud solutions.  The industry refers to that integration using a variety of buzzwords from hybrid cloud to software defined data center/storage/networking/etc.  I prefer a more simple definition of legacy solutions versus modern solutions.

So what do I mean by a modern solution?  I’m speaking of solutions with the following most if not all of these characteristics:

  • Customer maintains only the layers of the technology that directly present business value
  • Short time to market for new features and features are introduced in a “toggle on and toggle off” manner
  • Supports modern authentication, authorization, and identity management standards and specifications such as Open ID Connect, OAuth, SAML, and SCIM
  • On-demand scaling
  • Provides a robust web-based API
  • Customer data can exist on-premises or off-premises

Since I love the identity realm, I’m going to focus on the bullet regarding modern authentication, authorization, and identity management.  For this series of posts I’m going to look at how Microsoft’s Active Directory Federation Service (AD FS)  and Microsoft’s Web Application Proxy (WAP) can be used to help facilitate the use of modern authentication and authorization.

So where does AD FS and the WAP come in?  AD FS provides us with a security token service producing the logical security tokens used in SAML, OAuth, and Open ID Connect.  Why do we care about the MS WAP?  The WAP acts a reverse proxy giving us the ability to securely expose AD FS to untrusted networks (like the Internet) so that devices outside our traditional firewalled security boundary can leverage our modern authentication and authorization solution.

Some real life business cases that can be solved with this solution are:

  1. Single sign-on (SSO) experience to a SaaS application such as SharePoint online from both an Active Directory domain-joined endpoint or a non-domain joined endpoint such as a mobile phone.
  2. Limit the number of passwords a user needs to remember to access both internal and cloud applications.
  3. Provide authentication or authorization for modernized internal applications for endpoints outside the traditional firewalled security boundary.
  4. Authentication and authorization of devices prior to accessing an internal or cloud application.

As we can see from the above, there are some great benefits around SSO, limiting user credentials to improve security and user experience, and taking our authorization to the next step by doing contextual-based authorization (device information, user location, etc) versus relying upon just Active Directory group.

Microsoft does a relatively decent job describing how to design and implement your AD FS and WAP rollout, so I’m not going to cover much of that in this series.  Instead I’m going to focus on the “behind the scenes” conversations that occur with endpoints, WAP, AD FS, AD DS, and Azure AD. Before I begin delving into the weeds of the product, I’m going to spend this post giving an overview of what my lab looks like.

I recently put together a more permanent lab consisting of a mixture of on-premise VMs running on HyperV and Azure resources.  I manage to stay well within my $150.00 MSDN balance by keeping a majority of the VMs deallocated.   The layout of the lab is diagramed below.

HomeLab

 

On-premises I am running a small collection of Windows Server 2016 machines within HyperV running on top of Windows Server 2016.  I’m using a standard setup of an AD DS, AD CS, AADC, AD FS, and IIS/MS SQL server.  Running in Azure I have a single VNet with three subnets each separated by a network security group.  My core infrastructure of an AD DS, IIS/MS SQL, and AD FS server exist in my Intranet subnet with my DMZ subnet containing a single WAP.

The Active Directory configuration consists of a single Active Directory forest with an FQDN of journeyofthegeek.local.  The domain has been configured with an explicit UPN of journeyofthegeek.com which is assigned as the UPN suffix for all users synchronized to Azure Active Directory.  The domain is running in Windows Server 2016 domain and forest functional level.  The on-premises domain controller holds all FSMO roles and acts as the DC for the Active Directory site representing the on-premises physical location.  The domain controller in Azure acts as the sole DC for the Active Directory site representing Azure.  Both DCs host the split-brain DNS zone for journeyofthegeek.com.

The on-premises domain controller also runs Active Directory Certificate Services.  The CA is an enterprise CA that is used to distribute certificates to security principals in the environment.  I’ve removed the CDP from the certificate templates issued by the CA to eliminate complications with the CRL revocation checking.

The AD FS servers are members of an AD FS farm named sts.journeyofthegeek.com and use a MS SQL Server 2016 backend for storage of configuration information.  The SQL Server on-premises hosts the SQL instance that the AD FS users are using to store configuration information.

Azure Active Directory Connect is co-located on the AD FS server and uses the same SQL server as the AD FS uses.  It has been integrated with a lab Azure Active Directory tenant I use which has a few licenses of Office 365 Business Essentials.  The objectGUID attribute is used as the immutable ID and the Azure Active Directory tenant has the DNS namespaces of journeyofthegeek.onmicrosoft.com and journeyofthegeek.com associated with it.

The IIS server running in Azure runs a simple .NET application (https://blogs.technet.microsoft.com/tangent_thoughts/2015/02/20/install-and-configure-a-simple-net-4-5-sample-federated-application-samapp/) that is used for claims-based authentication.  I’ll be using that application for demonstrations with the Web Application Proxy and have used it in the past to demonstrate functionality of the Azure Application Proxy.

For the demonstrations throughout these series I’ll be using the following tools:

In my next post I’ll do a deep dive into what happens behind the scenes during the registration of the Web Application Proxy with an AD FS farm.  See you then!

 

Helpful hints for resolving AD FS problems – Part 2

Welcome back to part two of my series of posts which looks at resolving problems with AD FS.  You can check out part 1 here.  In this post I’ll look another problem you may encounter while administering the service.

With the introduction of AD FS 2012 R2, Microsoft de-coupled AD FS from IIS.  AD FS running on MS versions 2012 R2 or later now use the HTTP Server API (more often referred to as HTTP.SYS).  HTTP.SYS is a kernal mode drive that was introduced in Windows Server 2003 and is used by a Windows system to listen for HTTP and HTTPS requests (check out this article for a detailed breakdown of how it works.)  Infrastructure services such as IIS and WINRM use the driver.  By integrating AD FS directly with HTTP.SYS, Microsoft was able to cut the footprint of the solution by eliminating the need for IIS.  Awesome right?  Of course it is, however, it is a bit more challenging to troubleshoot.

Issue 2: Replacing the AD FS Service Communications certificate

The service communications certificate is one of the “big three” certificates used within an AD FS implementation.  The certificate that is assigned as the service communications certificate is used to protect web communication between clients and the AD FS service (i.e. SSL/TLS).  Like any certificate, it will have a standard lifecycle and will eventually need to be replaced.  When that time comes, you can run into a very interesting problem depending on how you go about replacing that certificate.

If you’ve been managing an AD FS instance for any period of time, you’ve more than likely become quite familiar with the AD FS Management Console.  When replacing the certificate in AD FS 2012 R2 or above, you may be tempted to use the Set Service Communications Certificate action seen below.  Let’s give it a try shall we?

ADFSMMCSC

I first requested a new web certificate from the instance of AD CS through the Certificate MMC and placed it in the Computer store.  I then granted READ access to the private key for the service account AD FS is using.  After that I used the Set Service Communications Certificate action and selected the new certificate.  A quick check of the thumbprint of the certificate now being used matches the thumbprint of the new certificate (pay attention to the thumbprint, I’ll reference it again later).  Last step is to restart the AD FS service.

Screen Shot 2017-06-10 at 3.12.06 PM.png

Let’s now test the sample claim app I described in my first post.

Screen Shot 2017-06-10 at 2.58.35 PM

Uh oh.  What happened?  A check of the Application, System, and AD FS Admin logs shows no errors or warning nor does the AD FS Debug after another attempt.  Heck, even the log for the HTTP.SYS kernal driver httperr.log in C:\Windows\System32\LogFiles\HTTPERR is empty.  This is yet another instance of where the answer could not be found in any of the logs I reviewed because it’s another error related to the integration with HTTP.SYS.  What to do next?

Much of the administration of the integration with HTTP.SYS is doing using netsh.  Here we’re going to look at the certificate bindings configured for the HTTP listeners using the command http showsslcert from the netsh command prompt.

Screen Shot 2017-06-10 at 3.07.19 PM.png

Well our bindings are there, but look at the thumbprint: 12506a00b40617b096002089383015bbbb99e970.  That thumbprint does not match the thumbprint for the new certificate I set for the Service Communications certificate.  So what happened?  My best guess is when one of the HTTPS listeners are hit, the configuration in the AD FS database does not match the configuration of the HTTP.SYS listeners causing AD FS to crash.  How do we fix it?  Come to find out from this blog, there is one additional command that needs to be run to setup the listeners with the proper bindings, Set-AdfsSslCertificate.  After using the Set-AdfsSslCertificate and setting it with the new thumbprint then restarting the AD FS service, netsh http showsslcert now shows the correct thumbprint and the sample claim app is now working as expected.

Screen Shot 2017-06-10 at 3.26.51 PM

What you should take from this post is that while integrating with HTTP.SYS helps to limit the AD FS footprint, it also adds some intricacies to troubleshooting the service when it stops working.  In the next and final post in this series I will cover an issue that can pop up when a Web Application Proxy (WAP) is integrated in the mix.

See you next post!

 

Helpful hints for resolving AD FS problems – Part 1

Hi everyone.

Over the past week I’ve been building a lab for an upcoming deep dive into Microsoft’s Web Application Proxy.  During the course of building the lab I ran into a few interesting issues with AD FS and the Web Application Proxy that I wanted to cover.  Some were similar to issues I’ve run into in production environments and some were new to me.

These issues are interesting in that there aren’t any obvious indicators of the problem in any of the typical logs.  Two out of three required some trial and error to determine root cause, while the third drove me quite insane for a good two weeks before getting an answer from an “official” source.  Over the course of this series of blogs I’ll cover each issue in detail with the hopes that it will help others troubleshoot these issues in the future.

Issue 1: AD FS Certificate authentication fails

I’m going to start with the problem that took me the longest to resolve and eventually required getting the answer directly from an official source.

For those of you that are unfamiliar, AD FS provides the capability to offer multi-factor authentication methods both native and third-party.  Out of the box, it supports certificate-based authentication as an option for a multi-factor or “step-up” authentication mechanism.

A few months back I wanted to take advantage of the certificate authentication feature to provide a two-factor authentication solution for applications integrated with AD FS.  Like a good engineer I did my Googling, read the Microsoft articles and various blogs out there to understand how the feature worked and what the requirements were.  I built a lab in Azure, setup an AD FS server, and ensured port 49443 was open in addition to the the typical ports required by AD FS.  I created my instance of AD CS, issued a user certificate containing the user’s UPN in the subject alternate name field, and setup a sample SAML app and configured it to require Certificate authentication.

How easy it all sounds right?  I navigated to the sample application and got the screen below…

Screen Shot 2017-06-04 at 9.29.35 PM

and I waited….  and waited…. and waited…  Ummm, what went wrong?  Well surely the AD FS log will tell me what happened.

Screen Shot 2017-06-04 at 9.34.03 PM.png

Well isn’t that odd.  No errors or warnings in the AD FS Admin log.  A quick check of the Application and System logs showed no errors either.  Maybe the AD FS Debug log would show me something?  I flipped on the log and attempted another authentication.

Screen Shot 2017-06-04 at 9.38.07 PM

Nothing as well?  Maybe the server can’t query the revocation lists designated in the certificates CDP?  Nope, not that either the server can successfully contact the CDP endpoints.  At this point I began to get quite frustrated and attempted packet captures, Fiddler captures, and anything and everything I could think of.  Nothing I tried revealed the answer.

I finally gave in (which I can tell you is incredibly challenging for me) and reached out to an “official” source.  We chatted back and forth and went through much of the same steps as outlined above to ensure I didn’t miss anything.  However, we ran into another dead end.  He then reached out to some other engineers he knew and eventually we got a hit.  We were told to check to see if there were any intermediary certificates stored within the trusted root certificate authorities store.  Sounds like an odd circumstance, but sure why not.

Upon opening up the certificates MMC, opening the machine store, and exploring the trusted root certificate authorities store low and behold I see an intermediary certificate within the store.  I deleted the certificate, restarted the AD FS server and attempted another login to the sample claim application and hit the screen below.

Screen Shot 2017-06-04 at 9.50.16 PM

Boom, I’m finally receiving the certificate prompt.  Clicking the OK button brings about the successful login below.

Screen Shot 2017-06-04 at 9.51.23 PM

So what was the issue?  Apparently AD FS certificate authentication fails without generating an error in any logical location (maybe nowhere at all?) if there is an intermediary certificate in the trusted root certificate authority machine store.  I’ve verified this is an issue in both AD FS 2012 R2 and AD FS 2016.  Now why this occurs is unknown to me.  It could be the underlining HTTPS.SYS driver that pukes and doesn’t report any errors to the event logs.  I didn’t get a straight answer as to why this occurs, just that it will due to some type of integrity check on the machine certificate store.  Odd right?

That completes the rundown of the first of three problems I’ll be outlining in this series of blogs.  Hopefully this helps save someone else some time and aggravation.

See you next post!

 

 

Active Directory Federation Services – SQL Attribute Store

Active Directory Federation Services – SQL Attribute Store

Hi everyone,

I recently had a use case come across my desk where I needed to do a SAML integration with a SaaS provider.  The provider required a number of pieces of information about the user beyond the standard unique identifier.  The additional information would be used to direct the user to the appropriate instance of the SaaS application.

In the past fifty or so SAML integrations I’ve done, I’ve been able to source my data directly from the Active Directory store.  This was because Active Directory was authoritative for the data or there was a reliable data synchronization process in place such that the data was being sourced from an authoritative source.  In this scenario, neither options was available.  Thankfully the data source I needed to hit to get the missing data exposed a subset of its data through a Microsoft SQL view.

I have done a lot in AD FS over the past few years from design to operational support of the service, but I had never sourced information from a data source hosted via MS SQL Server.  I reviewed the Microsoft documentation available via TechNet and found it to be lacking.  Further searches across MS blogs and third-party blogs provided a number of “bits” of information but no real end to end guide.  Given the lack of solid content, I decided it would be fun to put one together so off to Azure I went.

For the lab environment, I built the following:

  • Active Director forest name – geekintheweeds.com
  • Server 1 – SERVERDC (Windows Server 2016)
    • Active Directory Domain Services
    • Active Directory Domain Naming Services
    • Active Directory Certificate Services
  • Server 2 – SERVER-ADFS (Windows Server 2016)
    • Active Directory Federation Services
    • Microsoft SQL Server Express 2016
  • Server 3 – SERVER-WEB (Windows Server 2016)
    • Microsoft IIS

On SERVER-WEB I installed the sample claims application referenced here.  Make sure to follow the instructions in the blog to save yourself some headaches.  There are plenty of blogs out there that discuss building a lab consisting the of the services outlined above, so I won’t cover those details.

On SERVER-ADFS I created a database named hrdb within the same instance as the AD FS databases.  Within the database I created a table named dbo.EmployeeInfo with 5 columns named givenName, surName, email, userName, and role all of data type nvchar(MAX).  The userName column contained the unique values I used to relate a user object in Active Directory back to a record in the SQL database.

Screen Shot 2017-05-28 at 9.18.37 PM

Once the database was created and populated with some sample data and the appropriate Active Directory user objects were created, it was time to begin to configure the connectivity between AD FS and MS SQL.  Before we go creating the new attribute store, the AD FS service account needs appropriate permissions to access the SQL database.  I went the easy route and gave the service account the db_datareader role on the database, although the CONNECT and SELECT permissions would have probably been sufficient.

Screen Shot 2017-05-28 at 9.23.49 PM

After the service account was given appropriate permissions the next step was to configure it as an attribute store in AD FS.  To that I opened the AD FS management console, expanded the service node, and right-clicked on the Attribute Store and selected the Add Attribute Store option.  I used mysql  as the store name and selected SQL option from the drop-down box.  My SQL was a bit rusty so the connection string took a few tries to get right.

Screen Shot 2017-05-28 at 9.28.35 PM

I then created a new claim description to hold the role information I was pulling from the SQL database.

Screen Shot 2017-05-28 at 9.33.12 PM.png

The last step in the process was to create some claim rules to pull data from the SQL database.  Pulling data from a MS SQL datastore requires the use of custom claim rules.  If you’re unfamiliar with the custom claim language, the following two links are two of the best I’ve found on the net:

The first claim rule I created was a rule to query Active Directory via LDAP for the SAM-Account-Name attribute.  This is the attribute I would be using to query the SQL database for the user’s unique record.

Screen Shot 2017-05-28 at 9.42.05 PM.png

Next up I had my first custom claim rule where I queried the SQL database for the value in the userName column for the value of the SAM-Account-Name I pulled from earlier step and I requested back the value in the email column of the record that was returned. Since I wanted to do some transforming of the information in a later step, I added the claim to incoming claim set.

Screen Shot 2017-05-28 at 9.42.39 PM

I then issued another query for the value in the role column.

Screen Shot 2017-05-28 at 9.48.14 PM

Finally, I performed some transforms to verify I was getting the appropriate data that I wanted.  I converted the email address claim type to the Common Name type and the custom claim definition role I referenced above to the out of the box role claim definition.  I then hit the endpoint for the sample claim app and… VICTORY!

Screen Shot 2017-05-28 at 9.52.29 PM

Simple right?  Well it would be if this information had been documented within a single link.  Either way, I had some good lessons learned that I will share with you now:

  • Do NOT copy and paste claim rules.  I chased a number of red herrings trying to figure out why my claim rule was being rejected.  More than likely the copy/paste added an invalid character I was unable to see.
  • Brush up on your MS SQL before you attempt this.  My SQL was super rusty and it caused me to go down a number of paths which wasted time.  Thankfully, my worker Jeff Lee was there to add some brain power and help work through the issues.

Before I sign off, I want to thank my coworker Jeff Lee for helping out on this one.  It was a great learning experience for both of us.

Thanks and have a wonderful Memorial Day!

Azure AD Pass-through Authentication – How does it work? Part 2

Welcome back. Today I will be wrapping up my deep dive into Azure AD Pass-through authentication. If you haven’t already, take a read through part 1 for a background into the feature. Now let’s get to the good stuff.

I used a variety of tools to dig into the feature. Many of you will be familiar with the Sysinternals tools, WireShark, and Fiddler. The Rohitab API Monitor. This tool is extremely fun if you enjoy digging into the weeds of the libraries a process uses, the methods it calls, and the inputs and outputs. It’s a bit buggy, but check it out and give it a go.

As per usual, I built up a small lab in Azure with two Windows Server 2016 servers, one running AD DS and one running Azure AD Connect. When I installed Azure AD Connect I configured it to use pass-through authentication and to not synchronize the password. The selection of this option will the MS Azure Active Directory Application Proxy. A client certificate will also be issued to the server and is stored in the Computer Certificate store.

In order to capture the conversations and the API calls from the MS Azure Active Directory Application Proxy (ApplicationProxyConnectorService.exe) I set the service to run as SYSTEM. I then used PSEXEC to start both Fiddler and the API Monitor as SYSTEM as well. Keep in mind there is mutual authentication occurring during some of these steps between the ApplicationProxyConnectorService.exe and Azure, so the public-key client certificate will need to be copied to the following directories:

  • C:WindowsSysWOW64configsystemprofileDocumentsFiddler2
  • C:WindowsSystem32configsystemprofileDocumentsFiddler2

So with the basics of the configuration outlined, let’s cover what happens when the ApplicationProxyConnectorService.exe process is started.

  1. Using WireShark I observed the following DNS queries looking for an IP in order to connect to an endpoint for the bootstrap process of the MS AAD Application Proxy.DNS Query for TENANT ID.bootstrap.msappproxy.net
    DNS Response with CNAME of cwap-nam1-runtime.msappproxy.net
    DNS Response with CNAME of cwap-nam1-runtime-main-new.trafficmanager.net
    DNS Response with CNAME of cwap-cu-2.cloudapp.net
    DNS Response with A record of an IP
  2. Within Fiddler I observed the MS AAD Application Proxy establishing a connection to TENANT_ID.bootstrap.msappproxy.net over port 8080. It sets up a TLS 1.0 (yes TLS 1.0, tsk tsk Microsoft) session with mutual authentication. The client certificate that is used for authentication of the MS AAD Application Proxy is the certificate I mentioned above.
  3. Fiddler next displayed the MS AAD Application Proxy doing an HTTP POST of the XML content below to the ConnectorBootstrap URI. The key pieces of information provided here are the ConnectorID, MachineName, and SubscriptionID information. My best guess MS consumes this information to determine which URI to redirect the connector to and consumes some of the response information for telemetry purposes.Screen Shot 2017-04-05 at 9.37.04 PM
  4. Fiddler continues to provide details into the bootstrapping process. The MS AAD Application Proxy receives back the XML content provided below and a HTTP 307 Redirect to bootstrap.his.msappproxy.net:8080. My guess here is the process consumes this information to configure itself in preparation for interaction with the Azure Service Bus.Screen Shot 2017-04-05 at 9.37.48 PM
  5. WireShark captured the DNS queries below resolving the IP for the host the process was redirected to in the previous step.DNS Query for bootstrap.his.msappproxy.net
    DNS Response with CNAME of his-nam1-runtime-main.trafficmanager.net
    DNS Response with CNAME of his-eus-1.cloudapp.net
    DNS Response with A record of 104.211.32.215
  6. Back to Fiddler I observed the connection to bootstrap.his.msappproxy.net over port 8080 and setup of a TLS 1.0 session with mutual authentication using the client certificate again. The process does an HTTP POST of the XML content  below to the URI of ConnectorBootstrap?his_su=NAM1. More than likely this his_su variable was determined from the initial bootstrap to the tenant ID endpoint. The key pieces of information here are the ConnectorID, SubscriptionID, and telemetry information.
    Screen-Shot-2017-04-05-at-9.35.52-PM
  7. The next session capture shows the process received back the XML response below. The key pieces of content relevant here are within the SignalingListenerEndpointSettings section.. Interesting pieces of information here are:
    • Name – his-nam1-eus1/TENANTID_CONNECTORID
    • Namespace – his-nam1-eus1
    • ServicePath – TENANTID_UNIQUEIDENTIFIER
    • SharedAccessKey

    This information is used by the MS AAD Application Proxy to establish listeners to two separate service endpoints at the Azure Service Bus. The proxy uses the SharedAccessKeys to authenticate to authenticate to the endpoints. It will eventually use the relay service offered by the Azure Service Bus.

    Screen Shot 2017-04-05 at 9.34.43 PM

  8. WireShark captured the DNS queries below resolving the IP for the service bus endpoint provided above. This query is performed twice in order to set up the two separate tunnels to receive relays.DNS Query for his-nam1-eus1.servicebus.windows.net
    DNS Response with CNAME of ns-sb2-prod-bl3-009.cloudapp.net
    DNS Response with IP

    DNS Query for his-nam1-eus1.servicebus.windows.net
    DNS Response with CNAME of ns-sb2-prod-dm2-009.cloudapp.net
    DNS Response with different IP

  9. The MS AAD Application Proxy establishes connections with the two IPs received from above. These connections are established to port 5671. These two connections establish the MS AAD Application Proxy as a listener service with the Azure Service Bus to consume the relay services.
  10. At this point the MS AAD Application Proxy has connected to the Azure Service Bus to the his-nam1-cus1 namespace as a listener and is in the listen state. It’s prepared to receive requests from Azure AD (the sender), for verifications of authentication. We’ll cover this conversation a bit in the next few steps.When a synchronized user in the journeyofthegeek.com tenant accesses the Azure login screen and plugs in a set of credentials, Azure AD (the sender) connects to the relay and submits the authentication request. Like the initial MS AAD Application Proxy connection to the Azure Relay service, I was unable to capture the transactions in Fiddler. However, I was able to some of the conversation with API Monitor.

    I pieced this conversation together by reviewing API calls to the ncryptsslp.dll and looking at the output for the BCryptDecrypt method and input for the BCryptEncrypt method. While the data is ugly and the listeners have already been setup, we’re able to observe some of the conversation that occurs when the sender (Azure AD) sends messages to the listener (MS AAD Application Proxy) via the service (Azure Relay). Based upon what I was able to decrypt, it seems like one-way asynchronous communication where the MS AAD Application Proxy listens receives messages from Azure AD.

    Screen Shot 2017-04-05 at 9.38.40 PM

  11. The LogonUserW method is called from CLR.DLL and the user’s user account name, domain, and password is plugged. Upon a successful return and the authentication is valided, the MS AAD Application Proxy initiates an HTTP POST to
    his-eus-1.connector.his.msappproxy.net:10101/subscriber/connection?requestId=UNIQUEREQUESTID. The post contains a base64 encoded JWT with the information below. Unfortunately I was unable to decode the bytestream, so I can only guess what’s contained in there.{“JsonBytes”:[bytestream],”PrimarySignature”:[bytestream],”SecondarySignature”:null}

So what did we learn? Well we know that the Azure AD Pass-through authentication uses multiple Microsoft components including the MS AAD Application Proxy, Azure Service Bus (Relay), Azure AD, and Active Directory Domain Services. The authentication request is exchanged between Azure AD and the ApplicationProxyConnectorService.exe process running on the on-premises server via relay function of the Azure Service Bus.

The ApplicationProxyConnectorService.exe process authenticates to the URI where the bootstrap process occurs using a client certificate. After bootstrap the ApplicationProxyConnectorService.exe process obtains the shared access keys it will use to establish itself as a listener to the appropriate namespace in the Azure Relay. The process then establishes connection with the relay as a listener and waits for messages from Azure AD. When these messages are received, at the least the user’s password is encrypted with the public key of the client certificate (other data may be as well but I didn’t observe that).

When the messages are decrypted, the username, domain, and password is extracted and used to authenticate against AD DS. If the authentication is successful, a message is delivered back to Azure AD via the MS AAD Application Proxy service running in Azure.

Neato right? There are lots of moving parts behind this solution, but the finesse in which they’re integrated and executed make them practically invisible to the consumer. This is a solid out of the box solution and I can see why Microsoft markets in the way it does. I do have concerns that the solution is a bit of a black box and that companies leveraging it may not understand how troubleshoot issues that occur with it, but I guess that’s what Premier Services and Consulting Service is for right Microsoft? 🙂

Azure AD Pass-through Authentication – How does it work? Part 1

Hi everyone. I decided to take a break from the legacy and jump back to modern. Today I’m going to do some digging into Microsoft’s Azure AD Pass-through Authentication solution. The feature was introduced into public preview in December of 2016 and was touted as the simple and easy alternative to AD FS. Before I jump into the weeds of pass-through authentication, let’s do a high level overview of each option.

I will first cover the AD FS (Active Directory Federation Services) solution. When AD FS is used a solution for authentication to Azure Active Directory, it’s important to remember that AD FS is simply a product that enables the use of a technology to solve a business problem. In this instance the technology we are using is modern authentication (sometimes referred to as claims-based authentication) to solve the business problem of obtaining some level of assurance that a user is who they say they are.

When Azure AD and AD FS are integrated to enable the use of modern authentication, the Windows Services Federation Language (WS-FED) standard is used. You are welcome to read the standard for details, but the gist of WS-FED is a security token service generates logical security tokens (referred to assertions) which contain claims. The claims are typically pulled from a data store (such as Active Directory) and contain information about the user’s identity such as logon ID or email address. The data included in claims has evolved significantly over the past few years to include other data about the context of the user’s device (such as a trusted or untrusted device) and user’s location (coming from a trusted or untrusted IP range). The assertions are signed by the security token service (STS) and delivered to an application (referred to as the relying party) which validates the signature on the assertion, consumes the claims from the assertion, and authorizes the user access to the application.

You may have noticed above that we never talked about a user’s credentials. The reason for that is the user’s credentials aren’t included in the assertion. Prior to the STS generating the assertion, the user needs to authenticate to the STS. When AD FS is used, it’s common for the user to authenticate to the STS using Kerberos. Those of you that are familiar with Active Directory authentication know that a user obtains a Kerberos ticket-granting-ticket during workstation authentication to a domain-joined machine. When the user accesses AD FS (in this scenario the STS) the user provides a Kerberos service ticket. The process to obtain that service ticket, pass it to AD FS, getting an assertion, and passing that assertion back to the Azure AD (relying party in this scenario) is all seamless to the user and results in a true single sign-on experience. Additionally, there is no need to synchronize a user’s Active Directory Domain Services password to Azure AD, which your security folk will surely love.

The challenge presented with using AD FS as a solution is you have yet another service which requires on-premises infrastructure, must be highly available, and requires an understanding of the concepts I have explained above. In addition, if the service needs to be exposed to the internet and be accessible by non-domain joined machines, a reverse proxy (often Microsoft Web Application Proxy in the Microsoft world) which also requires more highly available infrastructure and the understanding of concepts such as split-brain DNS.

Now imagine you’re Microsoft and companies want to limit their on-premises infrastructure and the wider technology mark is slim in professionals that grasp all the concepts I have outlined above. What do you do? Well, you introduce a simple lightweight solution that requires little to no configuration or much understanding of what is actually happening. In come Azure AD Pass-through authentication.

Azure AD Pass-through authentication doesn’t require an STS or a reverse proxy. Nor does it require synchronization of a user’s Active Directory Domain Service password to Azure AD. It also doesn’t require making changes to any incoming flows in your network firewall. Sounds glorious right? Microsoft thinks this as well, hence why they’ve been pushing it so hard.

The user experience is very straightforward where the user plugs in their Active Directory Domain Services username and password at the Azure AD login screen. After the user hits the login screen, the user is logged in and go about their user way. Pretty fancy right? So how does Microsoft work this magic? It’s actually quite complicated but ingeniously implemented to seem incredibly simplistic.

The suspense is building right? Well, you’ll need to wait until my next entry to dig into the delicious details. We’ll be using a variety of tools including a simple packet capturing tool, a web proxy debugging tool, and an incredibly awesome API monitoring tool.

See you next post!