Deep Dive into Azure AD Domain Services – Part 3

Deep Dive into Azure AD Domain Services  – Part 3

Well folks, it’s time to wrap up this series on Azure Active Directory Domain Services (AAD DS).  In my first post I covered the basic configurations of the managed domain and in my second post took a look at how well Microsoft did in applying security best practices and complying with NIST standards.  In this post I’m going to briefly cover the LDAPS over the Internet capability, summarize some key findings, and list out some improvements I’d like to see made to the service.

One of the odd features Microsoft provides with the AAD DS service is the ability to expose the managed domain over LDAPS to the Internet.  I really am lost as to the use case that drove the feature.  LDAP is very much a legacy on-premises protocol that has no place being exposed to risks of the public Internet.  It’s the last thing that should the industry should be encouraging.  Just because you can, doesn’t mean you should.   Now let me step off the soap box and let’s take a look at the feature.

As I covered in my last post LDAPS is not natively enabled in the managed domain.  The feature must be configured and enabled through the Azure Portal.  The configuration consists of uploading the private key and certificate the service will use in the form of a PKCS12 file (*.PFX).  The certificate has a few requirements that are outlined in the instructions above.  After the certificate is validated, it takes about 10-15 minutes for the service to become available.  Beyond enabling the service within the VNet, you additionally have the option to expose the LDAPS endpoint to the Internet.

3aads1.png

Microsoft provides instructions on how to restrict access to the endpoint to trusted IPs via a network security group (NSG) because yeah, exposing an LDAP endpoint to the Internet is just a tad risky.  To lock it down you simply associate an NSG with the subnet AAD DS is serving.  Once that is done enable the service via the option in the image above and wait about 10 minutes.  After the service is up, register a external DNS record for the service that points to the IP address noted under the properties section of the AADS blade and you’re good to go.

For my testing purposes, I locked the external LDAPS endpoint down to the public IP address my Azure VM was SNATed to.  After that I created an entry in the host file of the VM that matched the external DNS name I gave the service (whyldap.geekintheweeds.com) to the public IP address of the LDAPS endpoint in order to bypass the split-brain DNS challenge.  Initiating a connection from LDP.EXE was a success.

3aads2.png

Now that we know the service is running, let’s check out what the protocol support and cipher suite looks like.

3aads3.png

Again we see the use of deprecated cipher suites. Here the risk is that much greater since a small mistake with an NSG could expose this endpoint directly to the Internet.  If you’re going to use this feature, please just don’t.  If you’re really determined to, don’t screw up your NSGs.

This series was probably one of the more enjoyable series I’ve done since I knew very little about the AAD DS offering. There were a few key takeaways that are worth sharing:

  • The more objects in the directory, the more expensive the service.
  • Users and groups can be created directly in managed domain after a new organizational unit is created.
  • Password and lockout policy is insanely loose to the point where I can create an account with a three character password (just need to meet complexity requirements) and accounts never lockout.  The policy cannot be changed.
  • RC4 encryption ciphers are enabled and cannot be disabled.
  • NTLMv1 is enabled and cannot be disabled.
  • The service does not support smart-card enforced users.  Yes, that includes both the users synchronized from Azure AD as well as any users you create directly in the managed domain.  If I had to guess, it’s probably due to the fact that you’re not a Domain Admin so hence you can’t add to the NTAuth certificate store.
  • LDAPS is not enabled by default.
  • Schema extensions are not supported.
  • Account-Based Kerberos Delegation is not supported.
  • If you are syncing identities to Azure AD, you’ll also need to synchronize your passwords.
  • The managed domain is very much “out of the box” defaults.
  • Microsoft creates a “god” account which is a permanent member of every privileged group in the forest
  • Recovery of deleted objects created directly in the managed domain is not possible.  The rights have not been delegated to the AADC Administrator.
  • The service does not allow for Active Directory trusts
  • SIDHistory attribute of users and groups sourced from Azure AD is populated with Primary Group from on-premises domain

My verdict on AAD DS is it’s not a very useful service in its current state.  Beyond small organizations, organizations that have very little to no requirements on legacy infrastructure, organizations that don’t have strong security requirements, and dev/qa purposes I don’t see much of a use for it right now.  It comes off as a service in its infancy that has a lot of room to grow and mature.  Microsoft has gone a bit too far in the standardization/simplicity direction and needs to shift a bit in the opposite direction by allowing for more customization, especially in regards to security.

I’d really like to see Microsoft introduce the capabilities below.   All of them should  exposed via the resource blade in the Azure Portal if at all possible.  It would provide a singular administration point (which seems to be the strategy given the move of Azure AD and Intune to the Azure Portal) and would allow Microsoft to control how the options are enabled in the managed domain.  This means no more administrators blowing up their Active Directory forest because they accidentally shut off all the supported cipher suites for Kerberos.

  • Expose Domain Controller Event Logs to Azure Portal/Graph API and add support for AAD DS Power BI Dashboards
  • Support for Active Directory trusts
  • Out of the box provide a Red Forest model (get rid of that “god” account)
  • Option to disable risky cipher suites for both Kerberos and LDAPS
  • Option to harden the password and lockout policy
  • Option to disable NTLMv1
  • Option to turn on LDAP Debug Logging
  • Option to direct Domain Controller event logs to a SIEM
  • Option to restore deleted users and groups that were created directly in the managed domain.  If you’re allow creation, you need to allow for restoration.
  • Removal of Internet-accessible LDAPS endpoint feature or at least somehow incorporate the NSG lockdown feature directly into the AAD DS blade.

While the service has a lot of room for improvement the direction of a managed Windows AD offering is spot on.  In the year 2018, there is no reason Windows AD shouldn’t be offered as a managed service.  The direction Microsoft has gone by sourcing the identities and credentials from Azure AD is especially creative.  It’s a solid step in the direction of creating a singular centralized identity service that provides both legacy and modern protocols.  I’ll be watching this service closely as Microsoft builds upon it for the next few months.

Thanks and see you next post!

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!

Azure AD ASP .NET Web Application

Hi all. Before I complete my series on Azure AD Provisioning with a look at how provisioning works with the Graph API, I want to take a detour and cover some Microsoft Visual Studio. Over the past month I’ve been spending some time building very basic applications.

As I’ve covered previously in my blog, integration is going to the primary responsibility of IT Professionals as more infrastructure shifts to the cloud. Our success at integration will largely depend on how well we understand the technologies, our ability to communicate what business problems these technologies can solve, and our understanding of how to help developers build applications to consume these technologies. In my own career, I’ve spent a significant time on all of the above except the last piece. That is where I’m focusing now.

Recently I built a small.NET forms application that integrated with the new Azure AD B2B API. Over the past few days I’ve been spending time diving with to ASP .NET Web Applications built with an MVC architecture. I decided to build an small MVC application that performed queries against the Graph API, and wow was it easy. There was little to no code that I had to provide myself and “it just worked”. You can follow these instructions if you’d like to play with it as well. If you’ve read this blog, you know I don’t do well with things that just work. I need to know how it works.

If you follow the instructions in the above link you will have a ASP .NET Web Application that is integrated with your Azure AD tenant, uses Azure AD for authentication via the Open ID Connect protocol, and is capable of reading directory data from the Graph API uses OAuth 2.0. So how is all this accomplished? What actually happened? What protocol is being used for authentication, how does the application query for directory data? Those are the questions I’ll focus on answering in this blog post.

Let’s first answer the question as to what Visual Studio did behind the scenes to integrate the application with Azure AD. In the explanation below I’ll be using the technology terms (OAuth 2.0 and Open ID Connect) in parentheses to translate the Microsoft lingo. During the initialization process Visual Studio communicated with Azure AD (Authorization Server) and registered (registration) the application (confidential client) with Azure AD as a Web App and gave it the delegated permissions (scopes) of “Sign in and read user profile” and “Read directory data”.

In addition to the registration of the application in Azure AD, a number of libraries and code have been added to the project that make the authentication and queries to the Graph API “out of the box”. All of the variables specific to the application such as Client ID, Azure AD Instance GUID, application secret key are stored in the web.config. The Startup.cs has the simple code that adds Open ID Connect authentication. Microsoft does a great job explaining the Open ID Connect code here. In addition to the code to request the Open ID Connect authentication, there is code to exchange the authorization code for an access token and refresh token for the Graph API as seen below with my comments.

AuthorizationCodeReceived = (context) =>
{
var code = context.Code;
// MF -> Create a client credential object with the Client ID and Application key
ClientCredential credential = new ClientCredential(clientId, appKey);
// MF -> Extract the access token from cache and generate an authentication context from it
string signedInUserID = context.AuthenticationTicket.Identity.FindFirst(ClaimTypes.NameIdentifier).Value;
AuthenticationContext authContext = new AuthenticationContext(Authority, new ADALTokenCache(signedInUserID));
// MF -> Acquire a token by submitting the authorization code, providing the URI that is registered for the application, the application secret key, and the resource (in this scenario the Graph API)
AuthenticationResult result = authContext.AcquireTokenByAuthorizationCode(
code, new Uri(HttpContext.Current.Request.Url.GetLeftPart(UriPartial.Path)), credential, graphResourceId);
return Task.FromResult(0);
}

Now that the user has authenticated and the application has a Graph API access token, I’ll hop over to the UserProfileController.cs. The code we’re concerned about in here is below with my comments.


{
Uri servicePointUri = new Uri(graphResourceID);
Uri serviceRoot = new Uri(servicePointUri, tenantID);
ActiveDirectoryClient activeDirectoryClient = new ActiveDirectoryClient(serviceRoot, async () => await GetTokenForApplication());
// MF -> Use the access token previous obtained to query the Graph API
var result = await activeDirectoryClient.Users.Where(u => u.ObjectId.Equals(userObjectID)).ExecuteAsync();
IUser user = result.CurrentPage.ToList().First();
return View(user);
}

Next I’ll hop over to the UserProfile view to look at the Index.cshtml. In this file a simple table is constructed that returns information about the user from the Graph API. I’ve removed some of the pesky HTML and replaced it with the actions.


@using Microsoft.Azure.ActiveDirectory.GraphClient
@model User
@{
ViewBag.Title = "User Profile";
}
"CREATE TABLE"
"TABLE ROW"
Display Name
@Model.DisplayName
"TABLE ROW"
First Name
@Model.GivenName
"TABLE ROW"
Last Name
@Model.Surname
"TABLE ROW"
Email Address
@Model.Mail

Simple right? I can expand that table to include any attribute exposed via the Graph API. As you can see in the above, I’ve added email address to the display. Now that we’ve reviewed the code, let’s cover the steps the application takes and what happens in each step:

  1. App accesses https://login.microsoftonline.com//.well-known/openid-configuration
    • Get OpenID configuration for Azure AD
  2. App accesses https://login.microsoftonine.com/common/discovery/keys
    • Retrieve public-keys used to verify signature of open id connect tokens
  3. User’s browser directed to https://login.microsoftonline.com//oauth2/authorize
    • Request an open id connect id token and authorization code for user’s profile information
  4. User’s browser directed to https://login.microsoftonline.com//login
    • User provides credentials to AAD and receives back
      1. id token
      2. access code for graph API with Directory.Read, User.Read scope
  5. User’s browser directed back to application
    • Return id token and access code to application
      1. id token authenticates user to application
      2. Access code for graph API with Directory.Read, User.Read scope temporarily stored
  6. Application accesses https://login.microsftonine.com//oauth2/token
    • Exchanges access code for bearer token
  7. Application sends OData query to Graph API and attaches bearer token.

That’s it folks! In my next post I will complete the Azure AD Provisioning series with a simple ASP .NET Web app that provisions new users into Azure AD.

Attribute Uniqueness in Azure Active Directory

As I dive deeper into Azure Active Directory, I am learning quickly that AAD is a very different animal than on-premises Active Directory Domain Services (AD DS). While both solutions provide identity, authentication, and authorization services, they do so in very different ways. These differences require organizations to be prepared to adjust standard processes to get the two services to work together. Today I will focus on the identity portion of the solution and how the different attribute uniqueness requirements in AAD and AD DS can introduce the need for evolution of management processes for AD DS.

The attributes I want to focus on are userPrincipalName, proxyAddresses, and mail. In AD DS userPrincipalName is a single valued attribute, proxyAddresses is a multivalued attribute, and the values included in those attributes must be unique to the object in the forest. The mail attribute (the attribute that populates the E-mail field on the General tab of Active Directory Users and Computers (ADUC)) is a single valued attribute that doesn’t have a uniqueness requirement. In AAD all three attributes retain their single value or multivalued properties, however, the uniqueness requirements change considerably.

AD DS allows these values to be duplicated across different attributes. For example, one object could have a userPrincipalName of john@contoso.com and another object could have a value in its proxyAddresses attribute of SMTP:john@contoso.com. The same goes for an object that has a mail attribute of john@contoso.com and another object has a value in its proxyAddresses of john@contoso.com.

In AAD this is no longer true. User, group, and contact objects synchronized to AAD from AD DS require the userPrincipalName, proxyAddresses, and mail (also targetAddresses if you’re using it) to be unique among all objects in the directory. This means that each of the scenarios I discussed above will create synchronization errors. You can’t have one user object with a value in the proxyAddresses of john@contoso.com and another use object with mail attribute of john@contoso.com.

What happens if you do? Well, let’s make it happen. In this scenario we have two user objects with the configuration below:

Object 1
userPrincipalName: jess.felton@journeyofthegeek.com
proxyAddresses: SMTP:felton@feltonma.com
Sync Status: Already synced to Azure AD

Object 2
userPrincipalName: matt.felton@journeyofthegeek.com
proxyAddresses:
mail: felton@feltonma.com
Sync Status: Not yet synced to Azure AD

After we force a delta synchronization of Azure AD Sync, the errors provided below pop up in Synchronization Manager and an email alert:

Screen-Shot-2016-06-05-at-8.07.18-PM.png

Screen-Shot-2016-06-05-at-8.08.24-PM

The net result of the above matt.felton@journeyofthegeek.com won’t synchronize correctly to AAD and the user will be unable to authenticate to AAD. How about two user objects with the same mail attribute? That’s a common use case, right? Nope, same issue. Take note that just because you receive an error saying the issue is with a duplicate value in the proxyaddresses attribute, it could be the userPrincipalName, mail, or targetAddress of another object in AD DS.

Small differences like this can lead to major changes in how organizations manage AD DS when they begin their journey into AAD. The key take away here is to understand that AD DS and AAD are not the same thing, the differences need to be understood, and you must be prepared to evolve existing processes if you wish to leverage the solution.

I’ll end this with a thank you to Jimmie Lightner from MS for his blog post that brought light to this issue many months ago. You can read that post here.

P.S. Take note that if you opt to an alternate login ID (separate attribute from userPrincipalName for user identifier in AAD), the uniqueness will carry over to that attribute as well.