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Duo adds two-factor authentication to Outlook Web App (OWA) logins, complete with inline self-service enrollment and Duo Prompt.
Check your server versions before starting. This supports Exchange Server 2010, running on Windows Server 2012 or newer. It also requires .NET Framework 3.5 and ASP.NET 3.5.
If you are running Exchange 2013 or later, see the Exchange Server 2013 and later Instructions.
This application communicates with Duo's service on TCP port 443. Firewall configurations that restrict outbound access to Duo's service with rules using destination IP addresses or IP address ranges aren't recommended, since these may change over time to maintain our service's high availability. If your organization requires IP-based rules, please review this Duo KB article.
Make sure you have installed .NET Framework 3.5. You can do this, for example, by running the following PowerShell commands:
Import-Module ServerManager
Add-WindowsFeature NET-Framework-Core
Also make sure you have installed ASP.NET 3.5 support for IIS and HTTP Activation. The PowerShell commands for this are:
Import-Module ServerManager
Add-WindowsFeature Web-Asp-Net
Add-WindowsFeature NET-HTTP-Activation
Ensure that the IIS Management Scripts and Tools feature is turned on as well. PowerShell example:
Import-Module ServerManager
Add-WindowsFeature Web-Scripting-Tools
Before moving on to the deployment steps, it's a good idea to familiarize yourself with Duo administration concepts and features like options for applications, available methods for enrolling Duo users, and Duo policy settings and how to apply them. See all Duo Administrator documentation.
The security of your Duo application is tied to the security of your secret key (skey). Secure it as you would any sensitive credential. Don't share it with unauthorized individuals or email it to anyone under any circumstances!
Try setting your application's "New user policy" to "Allow Access" while testing. Users that Duo knows about will be prompted to authenticate with Duo, while all other users will be transparently let through.
Users that have a phone (or hardware token) associated with them will see the authentication prompt. All other users will be able to add their phone through Duo's self-service enrollment (see Test Your Setup).
Then (when you're ready) change the "New user policy" to "Require Enrollment." This will prompt all users to authenticate (or enroll) after they type in their usernames and passwords.
Install Duo on the Microsoft Exchange Server instances running the Exchange 2010/2013 Client Access Server role or the Exchange 2016 Client Access services. The installation process varies slightly depending on how many Client Access servers you have. The Duo installer stops and then restarts IIS services on your Exchange servers automatically.
Launch the Duo Security installer MSI from an elevated command prompt (right-click "Command Prompt" and select the "Run as Administrator" option). Accept the license agreement and continue.
Enter your integration key, secret key, and API hostname when prompted.
If you leave the "Bypass Duo authentication when offline" box in the Duo installer checked, then your users will be able to logon without completing two-factor authentication if the Duo Security cloud service is unreachable. If that box is unchecked then all OWA login attempts will be denied if there is a problem contacting the Duo service.
Duo for OWA sends a user's Windows sAMAccountName to Duo's service by default. To send the userPrincipalName to Duo instead, check the Send username to Duo in UPN format box. For this to work, OWA and ECP must be using Forms-Based Authentication (FBA). Learn how to enable FBA for Exchange at Microsoft TechNet.
If you enable the UPN username format option, you must also change the properties of your OWA application in the Duo Admin Panel to change the "Username normalization" setting to None. Otherwise, Duo drops the domain suffix from the username sent from OWA to our service, which may cause user mismatches or duplicate enrollment.
If you only have one Exchange Server running the Client Access Server role, select the option to automatically generate a new key. However, if you have multiple Client Access Server servers then you should manually generate a random string at least 40 characters long, and use the same string as the session key during installation on each of the servers.
For example, you could use the following PowerShell commands to generate a suitable session key:
$bytes = new-object "System.Byte[]" 30
(new-object System.Security.Cryptography.RNGCryptoServiceProvider).GetBytes($bytes)
[Convert]::ToBase64String($bytes)
To test your setup, log into OWA. Duo's enrollment or login prompt should appear after you enter your username and password:
If you plan to permit use of WebAuthn authentication methods (security keys, U2F tokens, or Touch ID), Duo recommends enabling hostname whitelisting for this application and any others that show the inline Duo Prompt before onboarding your end-users.
Need some help? Take a look at the OWA Frequently Asked Questions (FAQ) page or try searching our OWA Knowledge Base articles or Community discussions. For further assistance, contact Support.
If your organization offloads SSL requests to OWA via a load balancer, please see the FAQ for additional Duo configuration instructions.
You can upgrade your Duo installation over the existing version; there's no need to uninstall first.
Download the most recent Duo OWA Installer Package for Exchange 2010 and run the MSI from an elevated command prompt. View checksums for Duo downloads here.
Follow the on-screen prompts to complete the upgrade installation. Note that the installer restarts IIS services.
Repeat the upgrade on all your Exchange client access servers.
