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Duo for Outlook Web App (OWA) on Exchange 2013 and Later

Duo adds two-factor authentication to Outlook Web App (OWA) logins, complete with inline self-service enrollment and Duo Prompt.

Walkthrough Video

 

Prerequisites

Check your server versions before starting. These instructions are for Exchange Server 2013 and 2016, running on Windows Server 2008 R2 or newer. It also requires .NET Framework 4.5 and ASP.NET 4.5.

If you are running Exchange 2010, see the Exchange Server 2010 Instructions. If you are running Exchange Server 2007, see the Exchange Server 2007 Instructions.

Connectivity Requirements

This integration communicates with Duo's service on TCP port 443. Also, we do not recommend locking down your firewall to individual IP addresses, since these may change over time to maintain our service's high availability.

  1. Make sure you have installed .NET Framework 4.5. You can do this, for example, by running the following PowerShell commands:

    Import-Module ServerManager
    Add-WindowsFeature NET-Framework-Core
    
  2. Also make sure you have installed ASP.NET 4.5 support for IIS and HTTP Activation. The PowerShell commands for this are:

    Import-Module ServerManager
    Add-WindowsFeature NET-Framework-45-ASPNET
    Add-WindowsFeature NET-WCF-HTTP-Activation45
    
  3. Ensure that the IIS Management Scripts and Tools feature is turned on as well. PowerShell example:

    Import-Module ServerManager
    Add-WindowsFeature Web-Scripting-Tools
    

First Steps

  1. Sign up for a Duo account.
  2. Log in to the Duo Admin Panel and navigate to Applications.
  3. Click Protect an Application and locate Microsoft OWA in the applications list. Click Protect this Application to get your integration key, secret key, and API hostname. (See Getting Started for help.)
  4. Download the Duo OWA Installer Package for Exchange 2013+. View checksums for Duo downloads here.

Treat your secret key like a password

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!

Deployment Tip

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.

Run the Installer

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.

  1. 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.

  2. Enter your integration key, secret key, and API hostname when prompted.

    Enter Duo Information

    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.

  3. 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.

    Create Session Key

    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)
    
  4. Complete the Duo installation. The installer stops and then restarts IIS services automatically.

Test Your Setup

To test your setup, log into OWA. Duo's enrollment or login prompt should appear after you enter your username and password:

Duo Prompt

Troubleshooting

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.

Advanced Configuration

If your organization offloads SSL requests to OWA via a load balancer, please see the FAQ for additional Duo configuration instructions.

Updating Duo for OWA

You can upgrade your Duo installation over the existing version; there's no need to uninstall first.

  1. Download the most recent Duo OWA Installer Package for Exchange 2013+ and run the MSI from an elevated command prompt. View checksums for Duo downloads here.

  2. Follow the on-screen prompts to complete the upgrade installation. Note that the installer restarts IIS services.

  3. Repeat the upgrade on all your Exchange client access servers.

Network Diagram

  1. OWA connection initiated
  2. Primary authentication
  3. Exchange Client Access connection established to Duo Security over TCP port 443
  4. Secondary authentication via Duo Security’s service
  5. Exchange Client Access receives authentication response
  6. OWA session logged in

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