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Duo for Citrix Gateway - nFactor Instructions

Last Updated: August 30th, 2021

Duo integrates with your on-premises Citrix Gateway to add two-factor authentication to remote access logins by utilizing the Advanced Authentication Policy framework. Duo Security supports inline self-service enrollment and Duo Prompt when logging on to the Citrix Gateway.


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.

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

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.

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.

If your users need the ability to reset passwords from the Citrix Gateway and your Citrix edition license or Gateway build does not permit use of nFactor, see the Citrix Gateway Basic Secondary Instructions.

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

Connectivity Requirements

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.

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 Citrix Gateway users before you begin to deploy Duo.

To integrate Duo with your Citrix Gateway, 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 Citrix Gateway and then contact Duo's cloud service for secondary authentication.

Locate (or set up) a system on which you will install the Duo Authentication Proxy. The proxy supports these operating systems:

  • Windows Server 2012 or later (Server 2016+ recommended)
  • CentOS 7 or later (CentOS 8+ recommended)
  • Red Hat Enterprise Linux 7 or later (RHEL 8+ recommended)
  • Ubuntu 16.04 or later (Ubuntu 18.04+ recommended)
  • Debian 7 or later (Debian 9+ recommended)

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.
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!

Install the Duo Authentication 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).

  1. Download the most recent Authentication Proxy for Windows from Note that the actual filename will reflect the version e.g. duoauthproxy-5.5.0.exe. View checksums for Duo downloads here.
  2. Launch the Authentication Proxy installer on the target Windows server as a user with administrator rights and follow the on-screen prompts.

To perform a silent install on Windows, issue the following from an elevated command prompt after downloading the installer (replacing version with the actual version you downloaded):

duoauthproxy-version.exe /S
  1. Ensure that Perl and a compiler toolchain are installed. On most recent RPM-based distributions — like Fedora, RedHat Enterprise, and CentOS — you can install these by running (as root):

    $ yum install gcc make libffi-devel perl zlib-devel diffutils

    On Debian-derived systems, install these dependencies by running (as root):

    $ apt-get install build-essential libffi-dev perl zlib1g-dev
  2. Download the most recent Authentication Proxy for Unix from From the command line you can use curl or wget to download the file, like $ wget --content-disposition Depending on your download method, the actual filename may reflect the version e.g. duoauthproxy-5.5.0-src.tgz. View checksums for Duo downloads here.

  3. Extract the Authentication Proxy files and build it as follows:

    $ tar xzf duoauthproxy-latest-src.tgz
    $ cd duoauthproxy-version-src
    $ make
  4. Install the authentication proxy (as root):

    $ cd duoauthproxy-build
    $ ./install

    Follow the prompts to complete the installation. The installer creates a user to run the proxy service and a group to own the log directory and files. You can accept the default user and group names or enter your own.

If you ever need to uninstall the proxy, run /opt/duoauthproxy/uninstall.

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:

Operating System Authentication
Proxy Version
Windows v5.0.0 and later C:\Program Files\Duo Security Authentication Proxy\conf\authproxy.cfg
Windows v4.0.2 and earlier C:\Program Files (x86)\Duo Security Authentication Proxy\conf\authproxy.cfg
Linux All /opt/duoauthproxy/conf/authproxy.cfg

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:


Individual properties beneath a section appear as:


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. 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.


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 Citrix Gateway

Next, you need to set up the Authentication Proxy to work with your Citrix Gateway or NetScaler. Create a [radius_server_iframe] section and add the properties listed below. If you've already set up the Duo Authentication Proxy for a different RADIUS iframe application, append a number to the section header to make it unique, like [radius_server_iframe2].

type Set to citrix_netscaler_rfwebui. Requires Authentication Proxy v3.1.0 and NS build 12.1-51.16 or later.
api_host Your API hostname (i.e.
ikey Your Duo Citrix NetScaler integration key
skey Your Duo Citrix NetScaler secret key
failmode Either safe or secure:
failmode Description
safe In the event that Duo's service cannot be contacted, users' authentication attempts will be permitted if primary authentication succeeds. (Default)
secure In the event that Duo's service cannot be contacted, all users' authentication attempts will be rejected.

The mechanism that the Authentication Proxy should use to perform primary authentication. This should correspond with the "client" section you created earlier.

duo_only_client Do not perform primary authentication. Make sure you have a [duo_only_client] section configured..

This parameter is optional if you only have one "client" section. If you have multiple, each "server" section should specify which "client" to use.

radius_ip_1 The management host IP address of your (first) Citrix Gateway or NetScaler
radius_secret_1 A secret to be shared between the proxy and your (first) Citrix Gateway or NetScaler
radius_ip_X (Optional) IP addresses of additional Citrix Gateway or NetScaler management hosts (specified as radius_ip_2, radius_ip_3, etc.)
radius_secret_X (Optional) Secrets shared with additional Citrix Gateways or NetScalers (specified as radius_secret_2, radius_secret_3, etc.)

Port on which to listen for incoming RADIUS Access Requests. If you have multiple RADIUS server sections you should use a unique port for each one.

Default: 1812

A completed config file, using duo_only_client so the NetScaler is the primary authenticator, should look something like:



Make sure to save your configuration file when done.


View video guides for proxy deployment at the Authentication Proxy Overview or see the Authentication Proxy Reference Guide for additional configuration options.

Start the Proxy

Open an Administrator command prompt and run:

net start DuoAuthProxy

Alternatively, open the Windows Services console (services.msc), locate "Duo Security Authentication Proxy Service" in the list of services, and click the Start Service button.

Authentication Proxy v5.1.0 and later includes the authproxyctl executable, which shows the connectivity tool output when starting the service. The installer adds the Authentication Proxy C:\Program Files\Duo Security Authentication Proxy\bin to your system path automatically, so you should not need to specify the full path to authproxyctl to run it.

From an administrator command prompt run:

authproxyctl start

If the service starts successfully, Authentication Proxy service output is written to the authproxy.log file, which can be found in the log subdirectory.

If you see an error saying that the "service could not be started", open the Application Event Viewer and look for an Error from the source "DuoAuthProxy". The traceback may include a "ConfigError" that can help you find the source of the issue.

Stop and restart the Authentication Proxy service by either clicking the Restart Service button in the Windows Services console or issuing these commands from an Administrator command prompt:

net stop DuoAuthProxy & net start DuoAuthProxy

To stop and restart the Authentication Proxy using authproxyctl, from an administrator command prompt run:

authproxyctl restart

Open a root shell and run:

# /opt/duoauthproxy/bin/authproxyctl start

To ensure the proxy started successfully, run:

# /opt/duoauthproxy/bin/authproxyctl status

Authentication Proxy service output is written to the authproxy.log file, which can be found in the log subdirectory.

To stop and restart the Authentication Proxy, open a root shell and run:

# /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.

Configure Your Citrix Gateway

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

Additionally, check your Citrix Gateway web portal theme. The inline, browser-based Duo Prompt is compatible with the "Default" (aka "Caxton"), "Green Bubbles", "X1", and "RFWebUI" NetScaler themes (as well as custom themes based on one of those built-in themes).

Learn more about customizing the Citrix Gateway User Portal.

When creating your Citrix Gateway custom theme, use one of these built-in themes as the base for your customizations.

Configure Authentication Actions

  1. Log in to the Citrix Gateway administrative interface.
  2. Navigate to SecurityAAA - Application TrafficPoliciesAuthenticationAdvanced PoliciesActionsRADIUS 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_iframe 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

    Add RADIUS server for RADIUS Action

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

Configure Authentication Policies

  1. Navigate to SecurityAAA - Application TrafficPoliciesAuthenticationAdvanced PoliciesPolicy 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.

    Add LDAP server for LDAP Authentication Policy

  3. Click Create.

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

    Add LDAP server for LDAP Authentication Policy

  5. Click Create.

Configure Policy Labels

  1. Navigate to SecurityAAA - Application TrafficPoliciesAuthenticationAdvanced PoliciesPolicy Label in the left panel of the administrative interface.
  2. Click Add.
  3. Name the Policy Label and click Continue.

    Add RADIUS server Authentication Policy Label

  4. Select RADIUS_DuoAuthenticationProxy as your Policy.

  5. Click Bind.

  6. Click Done.

Create an Authentication Virtual Server

  1. Navigate to SecurityAAA - Application TrafficVirtual 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.

    Add Authentication Virtual Server

  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 SecurityAAA - Application TrafficAuthentication 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.

    Add Authentication Profile

  4. Click Create.

Add Authentication Profile to Unified Gateway

  1. Navigate to Citrix GatewayVirtual 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".

    Add 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 enrollment/login prompt appears.

Citrix Gateway Authentication Prompt

Configure Allowed Hostnames

If you plan to permit use of WebAuthn authentication methods (security keys, U2F tokens, or Touch ID), Duo recommends configuring allowed hostnames for this application and any others that show the inline Duo Prompt before onboarding your end-users.

To test your setup with the Citrix Receiver or Workspace app, complete primary authentication. The Duo enrollment/login prompt appears.


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 Citrix Gateway
  2. Primary authentication using Active Directory or RADIUS
  3. Citrix Gateway 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. Citrix Gateway access granted