Using Duo for multi-factor authentication

Using Duo for multi-factor authentication#

Guacamole’s Duo authentication extension allows the third-party Duo service to be used as an additional authentication factor for users of your Guacamole installation. If installed, users that attempt to authenticate against Guacamole will be sent to Duo’s service for further verification.

Warning

You will need to restart the Guacamole web application in order to complete configuration. Doing this will disconnect all active users, so please:

  • Do this only at a time that you can tolerate service unavailability, such as a scheduled maintenance window.

  • Keep in mind that configuration errors may prevent Guacamole from starting back up.

Note

Guacamole’s Duo support cannot currently be used alongside single sign-on. If you use Duo and need both MFA and SSO support for Guacamole, you will need to either use your SSO provider’s own Duo integration or use TOTP instead of Duo.

How Duo works with Guacamole#

Duo is strictly a service for verifying the identities of users that have already been partially verified through another authentication method. Thus, for Guacamole to make use of Duo, at least one other authentication mechanism will need be configured, such as a supported database or LDAP.

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.

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 a “Web SDK” application, the information required to configure Guacamole is listed within the application’s “Details” section. You will need to copy the client ID, secret, and API hostname - they will later be specified within Guacamole’s configuration:

Installing/Enabling the Duo extension#

Guacamole is configured differently depending on whether Guacamole was installed natively or using the provided Docker images. The documentation here covers both methods.

Native installations of Guacamole under Apache Tomcat or similar are configured by modifying the contents of GUACAMOLE_HOME (Guacamole’s configuration directory), which is located at /etc/guacamole by default and may need to be created first:

  1. Download guacamole-auth-duo-1.6.0.tar.gz from the release page for Apache Guacamole 1.6.0 and extract it.

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

  3. Copy the guacamole-auth-duo-1.6.0.jar file from the contents of the archive to GUACAMOLE_HOME/extensions/.

  4. Proceed with the configuring Guacamole for the newly installed extension as described below. The extension will be loaded after Guacamole has been restarted.

Note

Download and documentation links for all officially supported extensions for a particular version of Guacamole are always provided in the release notes for that version. The copy of the documentation you are reading now is from Apache Guacamole 1.6.0.

If you are using a different version of Guacamole, please locate that version within the release archives and consult the documentation for that release instead.

Docker installations of Guacamole include a bundled copy of Apache Tomcat and are configured using environment variables. The startup process of the Docker image automatically populates GUACAMOLE_HOME (Guacamole’s configuration directory) based on the values of these variables.

If deploying Guacamole using Docker Compose:

You will need to add at least one relevant environment variable to the environment section of your guacamole/guacamole container, such as the DUO_ENABLED environment variable:

DUO_ENABLED: "true"
If instead deploying Guacamole by running docker run manually:

The same environment variable(s) will need to be provided using the -e option. For example:

$ docker run --name some-guacamole \
    -e DUO_ENABLED="true" \
    -d -p 8080:8080 guacamole/guacamole

If DUO_ENABLED is set to false, the extension will NOT be installed, even if other related environment variables have been set. This can be used to temporarily disable usage of an extension without needing to remove all other related configuration.

You don’t strictly need to set DUO_ENABLED if other related environment variables are provided, but the extension will be installed only if at least one related environment variable is set.

Required configuration#

If deploying Guacamole natively, you will need to add a section to your guacamole.properties that looks like the following:

duo-api-hostname: api-XXXXXXXX.duosecurity.com
duo-client-id: XXXXXXXXXXXXXXXXXXXX
duo-client-secret: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
duo-redirect-uri: https://myguac.example.net

The properties that must be set in all cases for any Guacamole installation using this extension are:

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 a “Web SDK” application, and can be found within the application details in the “API hostname” field. This value is required.

duo-client-id

The unique client ID provided for Guacamole by Duo. This value will have been generated by Duo when you added Guacamole as a “Web SDK” application, and can be found within the application details in the “Client ID” field. This value is required.

This value was formerly known as the “integration key” in older versions of Duo’s “Web SDK” and was configured with the duo-integration-key property in older versions of Guacamole.

duo-client-secret

The shared secret provided for Guacamole by Duo. This value will have been generated by Duo when you added Guacamole as a “Web SDK” application, and can be found within the application details in the “Client secret” field. This value is required.

This value was formerly known as the “secret key” in older versions of Duo’s “Web SDK” and was configured with the duo-secret-key property in older versions of Guacamole.

duo-redirect-uri

The URI that should be submitted to the Duo service such that they can redirect the authenticated user back to Guacamole after the authentication process is complete. This must be the full URL that a user would enter into their browser to access Guacamole. This value is required.

If deploying Guacamole using Docker Compose, you will need to add a set of environment variables to the environment section of your guacamole/guacamole container that looks like the following:

DUO_API_HOSTNAME: 'api-XXXXXXXX.duosecurity.com'
DUO_CLIENT_ID: 'XXXXXXXXXXXXXXXXXXXX'
DUO_CLIENT_SECRET: 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
DUO_REDIRECT_URI: 'https://myguac.example.net'

If instead deploying Guacamole by running docker run manually, these same environment variables will need to be provided using the -e option. For example:

$ docker run --name some-guacamole \
    -e DUO_API_HOSTNAME="api-XXXXXXXX.duosecurity.com" \
    -e DUO_CLIENT_ID="XXXXXXXXXXXXXXXXXXXX" \
    -e DUO_CLIENT_SECRET="XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX" \
    -e DUO_REDIRECT_URI="https://myguac.example.net" \
    -d -p 8080:8080 guacamole/guacamole

The environment variables that must be set in all cases for any Docker-based Guacamole installation using this extension are:

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 a “Web SDK” application, and can be found within the application details in the “API hostname” field. This value is required.

DUO_CLIENT_ID

The unique client ID provided for Guacamole by Duo. This value will have been generated by Duo when you added Guacamole as a “Web SDK” application, and can be found within the application details in the “Client ID” field. This value is required.

This value was formerly known as the “integration key” in older versions of Duo’s “Web SDK” and was configured with the duo-integration-key property in older versions of Guacamole.

DUO_CLIENT_SECRET

The shared secret provided for Guacamole by Duo. This value will have been generated by Duo when you added Guacamole as a “Web SDK” application, and can be found within the application details in the “Client secret” field. This value is required.

This value was formerly known as the “secret key” in older versions of Duo’s “Web SDK” and was configured with the duo-secret-key property in older versions of Guacamole.

DUO_REDIRECT_URI

The URI that should be submitted to the Duo service such that they can redirect the authenticated user back to Guacamole after the authentication process is complete. This must be the full URL that a user would enter into their browser to access Guacamole. This value is required.

Additional configuration (optional)#

The following additional, optional properties may be set as desired to tailor the behavior of the Duo support:

duo-auth-timeout

The maximum amount of time to wait for a user to finish authenticating with Duo, in minutes. Any authentication attempt that takes longer than this amount of time will be rejected, requiring the user to reenter their credentials and possibly revalidate their identity with Duo. By default, login attempts are allowed to take up to 5 minutes.

The following additional, optional environment variables may be set as desired to tailor the behavior of the Duo support:

DUO_AUTH_TIMEOUT

The maximum amount of time to wait for a user to finish authenticating with Duo, in minutes. Any authentication attempt that takes longer than this amount of time will be rejected, requiring the user to reenter their credentials and possibly revalidate their identity with Duo. By default, login attempts are allowed to take up to 5 minutes.

Bypass/Enforce Duo for Specific Hosts#

By default, when the Duo module is enabled, Duo-based MFA will be enforced for all users that attempt to log in to Guacamole, regardless of where they are connecting from. Depending on your use case, it may be necessary to narrow this behavior and only enforce Duo-based MFA for certain hosts and bypass it for others.

Warning

If you will be configuring Guacamole to consider users’ IP addresses, it is important to make sure that Guacamole is receiving correct IP address information for all clients.

If Guacamole is behind a reverse proxy, such as for SSL termination, the IP addresses of all users will appear to be the IP address of the proxy unless additional configuration steps are taken. Be sure to follow the documentation for configuring forwarding of client IP information!

Duo-based MFA can be explicitly bypassed or enforced on a per-host basis by providing the relevant, exhaustive list of addresses/networks using either of the following properties:

duo-bypass-hosts

A comma-separated list of all IP addresses and/or subnets (in CIDR notation) that SHOULD NOT be required to verify themselves with Duo when authenticating. All other hosts in this list will required to verify against Duo.

If both bypass and enforce lists are provided, the enforce list takes priority and this property is effectively ignored.

This property is optional. By default, verification against Duo will be required for all users regardless of their IP address (Duo is not bypassed for any addresses).

duo-enforce-hosts

A comma-separated list of all IP addresses and/or subnets (in CIDR notation) that SHOULD be required to verify themselves with Duo when authenticating. All other hosts will not be required to verify against Duo.

If both bypass and enforce lists are provided, the enforce list takes priority and the bypass list is effectively ignored.

This property is optional. By default, verification against Duo will be required for all users regardless of their IP address (Duo is enforced for all addresses).

By default, when the Duo module is enabled, Duo-based MFA will be enforced for all users that attempt to log in to Guacamole, regardless of where they are connecting from. Depending on your use case, it may be necessary to narrow this behavior and only enforce Duo-based MFA for certain hosts and bypass it for others.

Warning

If you will be configuring Guacamole to consider users’ IP addresses, it is important to make sure that Guacamole is receiving correct IP address information for all clients.

If Guacamole is behind a reverse proxy, such as for SSL termination, the IP addresses of all users will appear to be the IP address of the proxy unless additional configuration steps are taken. Be sure to follow the documentation for configuring forwarding of client IP information!

Duo-based MFA can be explicitly bypassed or enforced on a per-host basis by providing the relevant, exhaustive list of addresses/networks using either of the following environment variables:

DUO_BYPASS_HOSTS

A comma-separated list of all IP addresses and/or subnets (in CIDR notation) that SHOULD NOT be required to verify themselves with Duo when authenticating. All other hosts in this list will required to verify against Duo.

If both bypass and enforce lists are provided, the enforce list takes priority and this property is effectively ignored.

This property is optional. By default, verification against Duo will be required for all users regardless of their IP address (Duo is not bypassed for any addresses).

DUO_ENFORCE_HOSTS

A comma-separated list of all IP addresses and/or subnets (in CIDR notation) that SHOULD be required to verify themselves with Duo when authenticating. All other hosts will not be required to verify against Duo.

If both bypass and enforce lists are provided, the enforce list takes priority and the bypass list is effectively ignored.

This property is optional. By default, verification against Duo will be required for all users regardless of their IP address (Duo is enforced for all addresses).

Completing installation#

Guacamole will only reread its configuration and load newly-installed extensions during startup, so Tomcat will need to be restarted before these changes can take effect. Restart Tomcat and give the new functionality a try.

You do not need to restart guacd.

Hint

If Guacamole does not come back online after restarting Tomcat, check the logs. Configuration problems may prevent Guacamole from starting up, and any such errors will be recorded in Tomcat’s logs.

The environment variables that configure the behavior of Docker can only be set at the time the Docker container is created. To apply these configuration changes, you will need to recreate the container.

If your Guacamole container was deployed using Docker Compose:

Simply making the desired changes to your docker-compose.yml and running docker compose up is sufficient. Docker Compose will automatically recognize that the environment variables of the container have changed and recreate it.

If your Guacamole container was deployed manually (using docker run):

You wll need to manually use docker rm to remove the old container and then manually recreate it with docker run and the new environment variables.

Hint

If Guacamole does not come back online after recreating the container, check the Docker logs. Configuration problems may prevent Guacamole from starting up, and any such errors will be recorded in the Docker logs for the Guacamole container.

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