Duo for NetScaler - nFactor with RADIUS Challenge Text Prompt Instructions

Overview

To add Duo two-factor authentication to your Citrix Gateway with nFactor you'll configure the Duo Authentication Proxy as a secondary RADIUS authentication server. Primary authentication happens directly between the Citrix Gateway and your Active Directory, LDAP, or other identity store, which enables additional features such as AD password resets.

This configuration offers a text-based Duo prompt over RADIUS Challenge, and captures client IP information for use with Duo policies, such as geolocation and authorized networks.

If you have Citrix Gateway build 12.1-51.16 or later with an "Advanced" or "Premium" edition license, or Citrix Gateway build 13.0-67.x or later with "Standard", "Advanced", or "Premium" edition license, try Duo Single Sign-on for Citrix NetScaler, which includes Duo Universal Prompt support. This deployment option features Duo Single Sign-On, our cloud-hosted SSO identity provider. Primary and Duo secondary authentication occur at the identity provider, not at the NetScaler itself.

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

Prerequisites

Before starting, make sure that Duo is compatible with your Citrix Gateway device. Log on to your Citrix Gateway via the web interface and verify that your Citrix Gateway firmware is version 12.1-51.16 or later and your Citrix Receiver or Citrix Workspace clients support 12.1 or later. Citrix NetScaler 12.1 reached end of life on May 30, 2023, so we recommend updating your firmware to 13.0 or later.

Also verify that your Citrix Gateway is licensed for Advanced Authentication Policy. As of Citrix Gateway release 13.0-67.x, the "Standard" license also includes nFactor for Gateway/VPN, while Citrix ADC requires an "Advanced" or "Premium" license to use nFactor. Refer to the nFactor licensing in the Citrix documentation for more information.

Gateway appliances with standard licensing may need to enable the "Show unlicensed features" option under System → Licenses to expose the Advanced Authentication Policy items in the configuration menu.

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 operating systems for the system hosting the Duo Authentication Proxy:

• Windows Server 2016 or later
• CentOS 7
• CentOS Stream 8 or later
• Fedora 37 or later
• Red Hat Enterprise Linux 7 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.
3. Click Protect an Application and locate Citrix Gateway (NetScaler) 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, we'll set up the Authentication Proxy to work with your NetScaler. Create a [radius_server_challenge] section and add the properties listed below. If you've already set up the Duo Authentication Proxy for a different RADIUS Challenge application, append a number to the section header to make it unique, like [radius_server_challenge2].

Required

Optional

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

[duo_only_client]
 
[radius_server_challenge]
ikey=DIXXXXXXXXXXXXXXXXXX
skey=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
api_host=api-XXXXXXXX.duosecurity.com
failmode=safe
client=duo_only_client
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 Citrix Gateway

Before integrating with Duo, make sure your Citrix Gateway has a working Virtual Server with your preferred primary factor.

If you don't see the menu items in the following steps in your Citrix Gateway UI, refer back to the Prerequisites section to make sure you have the necessary Citrix Gateway license or firmware version, and that you've enabled view of the features.

Configure Authentication Actions

1. Log in to the Citrix Gateway administrative interface.

2. Navigate to Security → AAA - Application Traffic → Policies → Authentication → Advanced Policies → Actions → RADIUS in the left panel of the administrative interface.

3. Click Add to add your Duo Authentication Proxy server as an Authentication RADIUS server.

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

   Name	RADIUS_DuoAuthenticationProxy
   Server Name or IP Address	The hostname or IP address of your Duo Authentication Proxy server.
   Port	The port configured for radius_server_challenge 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

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

   

5. Click Create to add the RADIUS_DuoAuthenticationProxy RADIUS server and return to the "RADIUS Actions" page.

Configure Authentication Policies

1. Navigate to Security → AAA - Application Traffic → Policies → Authentication → Advanced Policies → Policy in the left panel of the administrative interface.

2. If you have no existing policy for your primary authentication click Add to add your primary authentication server. In this example primary authentication is done via an LDAP server.

   

3. Click Create.

4. Click Add to add your secondary authentication RADIUS Duo Authentication Proxy server.

   

5. Click Create.

Configure Policy Labels

1. Navigate to Security → AAA - Application Traffic → Policies → Authentication → Advanced Policies → Policy Label in the left panel of the administrative interface.

2. Click Add.

3. Name the Policy Label and click Continue.

   

4. Select RADIUS_DuoAuthenticationProxy as your Policy.

5. Click Bind.

6. Click Done.

Create an Authentication Virtual Server

1. Navigate to Security → AAA - Application Traffic → Virtual Servers in the left panel of the administrative interface.

2. Click Add.

3. Name the Authentication Virtual Server nFactor_Duo, select Non Addressable as your "IP Address Type" and click OK.

   

4. Choose or import the certificate for this virtual server.

5. Click No Authentication Policy and select your primary authentication server as the Policy.

6. Leave the "GoTo Expression" as NEXT and select RADIUS_DuoAuthenticationProxy as your "Next Factor" and click Bind.

7. Click Continue.

8. Click Done.

Create an Authentication Profile

1. Navigate to Security → AAA - Application Traffic → Authentication Profile in the left panel of the administrative interface.

2. Click Add.

3. Name the Authentication Profile nFactor_Duo and select nFactor_Duo as your Authentication Virtual Server.

   

4. Click Create.

Add Authentication Profile to Unified Gateway

1. Navigate to Citrix Gateway → Virtual Servers in the left panel of the administrative interface.

2. Select your existing Citrix Gateway Virtual Server, and then click Edit.

3. Click Authentication Profile within Advanced Settings in the right panel of the administrative interface.

4. Select nFactor_Duo as your "Authentication Profile".

   

5. Click OK.

6. Click Done.

7. Save all of the changes made to the running config.

Test Your Setup

To test your setup, browse to the URL you normally use to log in to your Citrix Gateway. After you complete primary authentication, the Duo RADIUS challenge text prompt lists your available factors, similar to this example:

Duo two-factor login for jdoe Enter a passcode or select one
of the following options: 1. Duo Push to XXX-XXX-1234 2. Phone
call to XXX-XXX-1234 3. SMS passcodes to XXX-XXX-1234 Passcode
or option (1-3)

In the text response area, type in the number that matches the option you want to use to log in. For example, to log in with Duo Push after receiving the above challenge prompt, enter 1, and then approve the Duo Push request you receive.

Instead of typing in the number that corresponds to the listed options, you may also enter a Duo factor option:

If you wanted to use Duo Push (rather than a passcode) to authenticate, you would enter:

push

You can also specify a number after the factor name if you have more than one device enrolled (as the automatic 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.

The format of the Duo RADIUS text challenge prompt may change if you have multiple authentication devices enrolled in Duo, due to the character length limit of a RADIUS packet. If we detect that the user logging in has too many devices to list by number with full details the Duo proxy will automatically switch to a compact format, like this.

Choose a secondary factor from (`push1`, `phone1`, `sms1`) or enter passcode:

Respond to this prompt in the same way, by typing in either the name of a Duo factor listed or a number that matches a factor's position in the list.

If you haven't already completed first-time Duo enrollment to set up your authentication devices, the RADIUS challenge text is a link to Duo enrollment. Copy the enrollment link and paste it into a web browser to complete Duo's enrollment process.

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 Citrix Gateway or 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. User completes Duo two-factor authentication via the RADIUS challenge from Duo's service with their selected authentication factor.
6. Duo Authentication Proxy receives authentication response
7. NetScaler access granted