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Chapter 8. Duo two-factor authentication

Guacamole supports Duo as a second authentication factor, layered on top of any other authentication extension, including those available from the main project website. The Duo authentication extension allows users to be additionally verified against the Duo service before the authentication process is allowed to succeed.

Important

This chapter involves modifying the contents of GUACAMOLE_HOME - the Guacamole configuration directory. If you are unsure where GUACAMOLE_HOME is located on your system, please consult Chapter 5, Configuring Guacamole before proceeding.

How Duo works with Guacamole

Guacamole provides support for Duo as a second authentication factor. To make use of the Duo authentication extension, some other authentication mechanism will need be configured, as well. When a user attempts to log into Guacamole, other installed authentication methods will be queried first:

Only after authentication has succeeded with one of those methods will Guacamole reach out to Duo to obtain additional verification of user identity:

If both the initial authentication attempt and verification through Duo succeed, the user will be allowed in. If either mechanism fails, access to Guacamole is denied.

Downloading the Duo extension

The Duo authentication extension is available separately from the main guacamole.war. The link for this and all other officially-supported and compatible extensions for a particular version of Guacamole are provided on the release notes for that version. You can find the release notes for current versions of Guacamole here: http://guacamole.incubator.apache.org/releases/.

The Duo authentication extension is packaged as a .tar.gz file containing only the extension itself, guacamole-auth-duo-0.9.13-incubating.jar, which must ultimately be placed in GUACAMOLE_HOME/extensions.

Installing Duo authentication

Guacamole extensions are self-contained .jar files which are located within the GUACAMOLE_HOME/extensions directory. To install the Duo authentication extension, you must:

  1. Create the GUACAMOLE_HOME/extensions directory, if it does not already exist.

  2. Copy guacamole-auth-duo-0.9.13-incubating.jar within GUACAMOLE_HOME/extensions.

  3. Configure Guacamole to use Duo authentication, as described below.

Important

You will need to restart Guacamole by restarting your servlet container in order to complete the installation. Doing this will disconnect all active users, so be sure that it is safe to do so prior to attempting installation. If you do not configure the Duo authentication properly, Guacamole will not start up again until the configuration is fixed.

Adding Guacamole to Duo

Duo does not provide a specific integration option for Guacamole, but Guacamole's Duo extension uses Duo's generic authentication API which they refer to as the "Web SDK". To use Guacamole with Duo, you will need to add it as a new "Web SDK" application from within the "Applications" tab of the admin panel of your Duo account:

Within the settings of the newly-added application, rename the application to something more representative than "Web SDK". This application name is what will be presented to your users when they are prompted by Duo for additional authentication:

Once you've finished adding Guacamole as an "Web SDK" application, the configuration information required to configure Guacamole is listed within the application's "Details" section. You will need to copy the integration key, secret key, and API hostname - they will later be specified within guacamole.properties:

Configuring Guacamole for Duo

The application-specific configuration information retrieved from Duo must be added to guacamole.properties to describe how Guacamole should connect to the Duo service:

duo-api-hostname

The hostname of the Duo API endpoint to be used to verify user identities. This will usually be in the form "api-XXXXXXXX.duosecurity.com", where "XXXXXXXX" is some arbitrary alphanumeric value assigned by Duo. This value will have been generated by Duo when you added Guacamole as an "Web SDK" application, and can be found within the application details in the "API hostname" field. This value is required.

duo-integration-key

The integration key provided for Guacamole by Duo. This value will have been generated by Duo when you added Guacamole as an "Web SDK" application, and can be found within the application details in the "Integration key" field. This value is required and must be EXACTLY 20 characters.

duo-secret-key

The secret key provided for Guacamole by Duo. This value will have been generated by Duo when you added Guacamole as an "Web SDK" application, and can be found within the application details in the "Secret key" field. This value is required and must be EXACTLY 20 characters.

In addition to the above, you must also manually generate an "application key". The application key is required by Duo's authentication API, but is not provided by Duo. It is an arbitrary value meant to be unique to each deployment of an application using their API.

duo-application-key

An arbitrary, random key which you manually generated for Guacamole. This value is required and must be AT LEAST 40 characters.

The application key can be generated with any method as long as it is sufficiently random. There exist utilities which will do this for you, like pwgen:

$ pwgen 40 1
em1io4zievohneeseiwah0zie2raQuoo2ci5oBoo
$

Alternatively, one quick and fairly portable way to do this is to use the dd utility to copy random bytes from the secure random device /dev/random, sending the data through a cryptographic hash tool with a sufficiently-long result, like sha256sum:

$ dd if=/dev/random count=1 | sha256sum
5d16d6bb86da73e7d1abd3286b21dcf3b3e707532e64ceebc7a008350d0d485d -
$

Completing the installation

Guacamole will only reread guacamole.properties and load newly-installed extensions during startup, so your servlet container will need to be restarted before Duo authentication will take effect. Restart your servlet container and give the new authentication a try.

Important

You only need to restart your servlet container. You do not need to restart guacd.

guacd is completely independent of the web application and does not deal with guacamole.properties or the authentication system in any way. Since you are already restarting the servlet container, restarting guacd as well technically won't hurt anything, but doing so is completely pointless.

If Guacamole does not come back online after restarting your servlet container, check the logs. Problems in the configuration of the Duo extension may prevent Guacamole from starting up, and any such errors will be recorded in the logs of your servlet container.