Duo for NetScaler - Basic Authentication with RADIUS Instructions

Overview

To add Duo two-factor authentication to your NetScaler you'll configure the Duo Authentication Proxy as a secondary RADIUS authentication server. Primary authentication happens directly between the NetScaler and your Active Directory, LDAP, or other identity store, which enables additional features such as AD password resets. Users will enter the name of a Duo factor or a passcode into a second password field when logging into the NetScaler.

This configuration captures client IP information for use with Duo policies, such as geolocation and authorized networks. This is a supported configuration for customers whose NetScaler devices do not meet the requirements for Duo Universal Prompt solutions.

If your NetScaler is licensed for Advanced Authentication Policy, and you want to offer your users a Duo experience with a text-based RADIUS challenge prompt, please see NetScaler nFactor RADIUS Challenge Instructions.

NetScaler was also known as Citrix Gateway. These instructions apply to both products.

Universal Prompt Solutions

If you have a NetScaler running 14.1-29.63 or later and Advanced or Premium licensing, please deploy Duo for NetScaler Web - OAuth.

If you have one of the following with a Citrix Federated Authentication Service (FAS) deployment:

• Citrix Gateway build 12.1-51.16 or later with an Advanced or Premium edition license
• Citrix Gateway build 13.0-67.x or later with an Standard, Advanced, or Premium edition license
• NetScaler 14 or later with Standard, Advanced, or Premium edition license

Try Duo Single Sign-on for NetScaler (FAS required).

Both the OIDC and the SSO solutions include Duo Universal Prompt support.

Learn more about the differences between Duo's NetScaler deployment configurations.

First Steps

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.

You should already have a working primary authentication configuration for your NetScaler users before you begin to deploy Duo.

To integrate Duo with your NetScaler, you will need to install a local Duo proxy service on a machine within your network. This Duo proxy server will receive incoming RADIUS requests from your NetScaler and then contact Duo's cloud service for secondary authentication.

If you are already running a Duo Authentication Proxy server in your environment, you can use that existing host for additional applications, appending the new configuration sections to the current config. You don't have to set up a new Authentication Proxy server for each application you create. However, there are some cases where it might make sense for you to deploy a new proxy server for a new application, like if you want to co-locate the Duo proxy with the application it will protect in the same data center.

We recommend the following 64-bit operating systems for the system hosting the Duo Authentication Proxy:

• Windows Server 2016 or later
• CentOS Stream 9 or later
• Fedora 39 or later
• Red Hat Enterprise Linux 7 or later
• Rocky Linux 9 or later
• Ubuntu 20.04 LTS or later
• Debian 11 or later

The Duo End of Sale, Last Date of Support, and End of Life Policy states that Duo does not offer support for integrations running on operating system versions beyond the vendor’s stated Last Date of Support date.

See detailed Authentication Proxy operating system performance recommendations in the Duo Authentication Proxy Reference.

We do not recommend installing the Duo Authentication Proxy on the same Windows server that acts as your Active Directory domain controller or one with the Network Policy Server (NPS) role. If you must co-locate the Duo Authentication Proxy with these services, be prepared to resolve potential LDAP or RADIUS port conflicts between the Duo service and your pre-existing services.

Then you'll need to:

1. Sign up for a Duo account.
2. Log in to the Duo Admin Panel and navigate to Applications → Protect an Application.
3. Locate the entry for NetScaler RADIUS with a protection type of "2FA" in the applications list. Click Protect to get your integration key, secret key, and API hostname. You'll need this information to complete your setup. See Protecting Applications for more information about protecting applications in Duo and additional application options.

Install the Duo Authentication Proxy

If you will reuse an existing Duo Authentication Proxy server for this new application, you can skip the install steps and go to Configure the Proxy.

The Duo Authentication Proxy can be installed on a physical or virtual host. We recommend a system with at least 1 CPU, 200 MB disk space, and 4 GB RAM (although 1 GB RAM is usually sufficient). See additional Authentication Proxy performance recommendations in the Duo Authentication Proxy Reference.

We do not recommend installing the Duo Authentication Proxy on the same Windows server that acts as your Active Directory domain controller or one with the Network Policy Server (NPS) role. If you must co-locate the Duo Authentication Proxy with these services, be prepared to resolve potential LDAP or RADIUS port conflicts between the Duo service and your pre-existing services.

duoauthproxy-version.exe /S

duoauthproxy-version.exe /S /exclude-auth-proxy-manager

sudo ./duoauthproxy-build/install --install-dir /opt/duoauthproxy --service-user duo_authproxy_svc --log-group duo_authproxy_grp --create-init-script yes

Configure the Proxy

After the installation completes, you will need to configure the proxy.

The Duo Authentication Proxy configuration file is named authproxy.cfg, and is located in the conf subdirectory of the proxy installation. With default installation paths, the proxy configuration file will be located at:

Note that as of v4.0.0, the default file access on Windows for the conf directory is restricted to the built-in Administrators group during installation.

The configuration file is formatted as a simple INI file. Section headings appear as:

[section]

Individual properties beneath a section appear as:

name=value

The Authentication Proxy may include an existing authproxy.cfg with some example content. For the purposes of these instructions, however, you should delete the existing content and start with a blank text file.

Duo Authentication Proxy Manager

The Duo Authentication Proxy Manager is a Windows utility for managing the Authentication Proxy installation on the Windows server where you install the Authentication Proxy. The Proxy Manager comes with Duo Authentication Proxy for Windows version 5.6.0 and later.

The Proxy Manager cannot manage remote Duo Authentication Proxy servers, nor can you install the Proxy Manager as a stand-alone application. There is no Proxy Manager available for Linux. The Proxy Manager only functions as part of a local Duo Authentication Proxy installation on Windows servers.

Learn more about using the Proxy Manager in the Duo Authentication Proxy Reference before you continue.

To launch the Proxy Manager utility:

• Open the Start Menu and go to Duo Security.
• Click the Duo Authentication Proxy Manager icon to launch the application. You must have administrative privileges on the Windows server and accept the prompt for elevation.
• The Proxy Manager launches and automatically opens the %ProgramFiles%\Duo Security Authentication Proxy\conf\authproxy.cfg file for editing.

Use the Proxy Manager editor on the left to make the authproxy.cfg changes in these instructions. As you type into the editor, the Proxy Manager will automatically suggest configuration options. Accepting these suggestions helps make sure you use the correct option syntax.

As you follow the instructions on this page to edit the Authentication Proxy configuration, you can click Validate to verify your changes (output shown on the right).

When you complete the Authentication Proxy configuration steps in this document, you can use the Save button to write your updates to authproxy.cfg, and then use the authproxy.cfg button to start the Authentication Proxy service before continuing on to the next configuration steps.

If you do not use the Proxy Manager to edit your configuration then we recommend using WordPad or another text editor instead of Notepad when editing the config file on Windows.

Configure the Proxy for Duo Only Authentication

At the top of your authproxy.cfg, create a [duo_only_client] section. This section has no additional parameters to configure.

[duo_only_client]

When using the [duo_only_client] configuration, the Authentication Proxy will ignore primary credentials and perform Duo factor authentication only.

Configure the Proxy for Your NetScaler

Next, you need to set up the Authentication Proxy to work with your NetScaler. Create a [radius_server_duo_only] section and add the properties listed below. If you've already set up the Duo Authentication Proxy for a different RADIUS Duo-only application, append a number to the section header to make it unique, like [radius_server_duo_only2].

Required

Optional

A completed config file for radius_server_duo_only with no primary authenticator should look something like:

[duo_only_client]
 
[radius_server_duo_only]
ikey=DIXXXXXXXXXXXXXXXXXX
skey=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
api_host=api-XXXXXXXX.duosecurity.com
failmode=safe
radius_ip_1=5.6.7.8
radius_secret_1=radiussecret1
port=1812

Make sure to save your configuration file in your text editor — or validate and save in the Proxy Manager for Windows — when you're finished making changes.

Start the Proxy

net start DuoAuthProxy

authproxyctl start

net stop DuoAuthProxy & net start DuoAuthProxy

authproxyctl restart

# /opt/duoauthproxy/bin/authproxyctl start

# /opt/duoauthproxy/bin/authproxyctl status

# /opt/duoauthproxy/bin/authproxyctl restart

If you modify your authproxy.cfg configuration after initial setup, you'll need to stop and restart the Duo Authentication Proxy service or process for your change to take effect.

You can view information about your Authentication Proxy in the Authentication Proxy Dashboard.

Configure Your NetScaler

Before integrating with Duo, make sure your NetScaler has a working virtual server with your preferred primary factor, such as LDAP against Active Directory.

Configure Secondary Factor

IMPORTANT: Citrix NetScaler 12.1 reached end of life on May 30, 2023, and NetScaler 13.0 reached end of life on July 15, 2024.

Duo does not support integrations beyond the third-party vendor's last date of support. Please review the Duo End of Sale, Last Date of Support, and End of Life Policy.

1. Log in to the NetScaler administrative interface.

2. Navigate to NetScaler Gateway → Virtual Servers or Citrix Gateway → Virtual Servers in the left panel of the administrative interface.

3. Select the existing Gateway Virtual Server to which you want to add Duo authentication, and then click Edit.

4. On the "VPN Virtual Server" page, click the plus sign (+) next to Basic Authentication to add a new authentication policy.

5. On the "Choose Type" page, select the RADIUS policy and Secondary type from the drop-down menus and click Continue.

   

6. On the next "Choose Type" screen, click the Add button or the plus sign (+) next to the "Policy Binding" → "Select Policy" box.

7. On the "Create Authentication RADIUS Policy" page, enter a name for the policy (like DuoRADIUS), and then click the Add button or the plus sign (+) next to the "Server" box to create a new RADIUS server for Duo authentication.

8. On the "Create Authentication RADIUS Server" page, enter the information for your Duo Authentication Proxy server:

   Name	Some descriptive name for the Duo server.
   Server Name or IP Address	The hostname or IP address of your Duo Authentication Proxy server.
   Port	The port configured for radius_server_duo_only on the Duo Authentication Proxy (1812 in the example).
   Time-out (seconds).	60
   Secret Key	The RADIUS secret shared with your Duo Authentication Proxy.
   Confirm Secret Key	The RADIUS secret shared with your Duo Authentication Proxy.
   Send Calling Station ID	Check this box in order to send the IP address of Citrix Receiver or Workspace clients to Duo.

   

   If you use the Citrix Workspace app, click on More and set the “Group Vendor Identifier" to 3825.

9. Click Create to add the new Duo RADIUS server and return to the "Create Authentication RADIUS Policy" page.

10. In the Expression box, enter ns_true.

11. When the "Server" and "Expression" information is correct click Create to save the new Duo RADIUS policy and return to the "Choose Type" page.

12. On the "Choose Type" page, make sure the new RADIUS authentication policy you just created is selected. Set the Priority under "Binding Details" to 100 and click Bind.

    

13. Binding the new authentication policy returns you to the "VPN Virtual Server" page.

14. Verify that your virtual server now has a new RADIUS policy present for secondary authentication, and that your original primary authentication policy is intact. Click Close to save the new policy configuration.

    

Test Your Setup

To test your setup, browse to the URL you normally use to log in to your NetScaler or connect with the Citrix Receiver or Workspace app. Enter your username and password, then enter the name of an out-of-band Duo authentication factor or a passcode generated by Duo Mobile or SMS in the "Password 2" field.

You may choose from the following Duo factor names for the second password:

You can also specify a number after the factor name if you have more than one device enrolled (as the push or phone call goes to the first capable device attached to a user). So you can enter phone2 or push2 if you have two phones enrolled and you want the authentication request to go to the second phone.

Note: Users of the Citrix Receiver or Workspace mobile app on iOS and Android may have issues connecting with this configuration. Please see the FAQ for additional instructions.

Troubleshooting

Need some help? Review troubleshooting tips for the Authentication Proxy and try the connectivity tool included with Duo Authentication Proxy 2.9.0 and later to discover and troubleshoot general connectivity issues.

Also take a look at the NetScaler Frequently Asked Questions (FAQ) page or try searching our Citrix NetScaler Knowledge Base articles or Community discussions. For further assistance, contact Support.

Network Diagram

1. Primary authentication initiated to NetScaler.
2. Primary authentication using Active Directory or RADIUS.
3. NetScaler sends authentication request to Duo Security’s authentication proxy.
4. Duo authentication proxy connection established to Duo Security over TCP port 443.
5. Secondary authentication via Duo Security’s service.
6. Duo Authentication Proxy receives authentication response.
7. NetScaler access granted.