Duo offers a variety of methods for adding two-factor authentication and flexible security policies to Slack SSO logins, complete with inline self-service enrollment and Duo Prompt.
Duo Access Gateway will reach end of life in October 2023. Customers may not create new DAG applications after May 19, 2022. Please see the Guide to Duo Access Gateway end of life for more details.
Use the Duo Single Sign-on for Slack application to protect Slack with Duo Single Sign-On, our cloud-hosted identity provider featuring Duo Central and the Duo Universal Prompt.
As business applications move from on-premises to cloud hosted solutions, users experience password fatigue due to disparate logons for different applications. Single sign-on (SSO) technologies seek to unify identities across systems and reduce the number of different credentials a user has to remember or input to gain access to resources.
While SSO is convenient for users, it presents new security challenges. If a user's primary password is compromised, attackers may be able to gain access to multiple resources. In addition, as sensitive information makes its way to cloud-hosted services it is even more important to secure access by implementing two-factor authentication and zero-trust policies.
Duo Access Gateway (DAG), our on-premises SSO product, layers Duo's strong authentication and flexible policy engine on top of Slack logins using the Security Assertion Markup Language (SAML) 2.0 authentication standard. Duo Access Gateway acts as an identity provider (IdP), authenticating your users using existing on-premises or cloud-based directory credentials and prompting for two-factor authentication before permitting access to Slack.
Duo Access Gateway is included in the Duo Premier, Duo Advantage, and Duo Essentials plans, which also include the ability to define policies that enforce unique controls for each individual SSO application. For example, you can require that Salesforce users complete two-factor authentication at every login, but only once every seven days when accessing Slack. Duo checks the user, device, and network against an application's policy before allowing access to the application.
Install Duo Access Gateway on a server in your DMZ. Follow our instructions for deploying the server, configuring DAG settings, and adding your primary authentication source.
Add the attributes from the table below that correspond to the Duo attributes Mail attribute, Last name attribute, and First name attribute in the "Attributes" field when configuring your Active Directory or OpenLDAP authentication source in the DAG admin console, separated by a comma. For example, if Active Directory is your authentication source, enter mail,sn,givenName in the "Attributes" field.
|Duo Attribute||Active Directory||OpenLDAP|
|First name attribute||givenName||gn|
|Last name attribute||sn||sn|
If your organization uses other directory attributes than the ones listed here then enter those attribute names instead. If you've already configured the attributes list for another cloud service provider, append the additional attributes not already present to the list, separated by a comma.
After completing the initial DAG configuration steps, click Applications on the left side of the Duo Access Gateway admin console.
Scroll down the Applications page to the Metadata section. This is the information you need to provide to Slack when configuring SSO. Click the Download Certificate link to obtain the token signing certificate (the downloaded file is named "dag.crt").
Log on to the Duo Admin Panel and navigate to Applications.
Click Protect an Application and locate the entry for Slack with a protection type of "2FA with SSO self-hosted (Duo Access Gateway)" in the applications list. Click Protect to the far-right to start configuring Slack. See Protecting Applications for more information about protecting applications in Duo and additional application options.
The Team name is the subdomain used when logging into your company's Slack site. For example, if your Slack team login URL is https://teamname.slack.com, enter teamname.
Slack uses the Mail attribute, First name attribute, and Last name attribute when authenticating. We've mapped those to DAG supported authentication source attributes as follows:
|Duo Attribute||Active Directory||OpenLDAP||SAML IdP||Azure|
|First name attribute||givenName||gn||givenName||given_name||givenName|
|Last name attribute||sn||sn||sn||family_name||surname|
If you are using non-standard attributes for your authentication source, check the Custom attributes box and enter the names of the attributes you wish to use instead.
Click Save Configuration to generate a downloadable configuration file.
You can adjust additional settings for your new SAML application at this time — like changing the application's name from the default value, enabling self-service, or assigning a group policy — or come back and change the application's policies and settings after you finish SSO setup. If you do update any settings, click the Save Changes button when done.
Click the Download your configuration file link to obtain the Slack application settings (as a JSON file).
Before you do this, verify that you updated the "Attributes" list for your Duo Access Gateway authentication source as specified here.
Return to the Applications page of the DAG admin console session.
Click the Choose File button in the "Add Application" section of the page and locate the Slack SAML application JSON file you downloaded from the Duo Admin Panel earlier. Click the Upload button after selecting the JSON configuration file.
The Slack SAML application is added.
Add the Duo Access Gateway as a new single sign-on provider for Slack.
Log on your Slack team site as an administrator. On the sidebar menu navigate to Administration → Authentication. Click the Configure link for "SAML authentication".
On the "Choose your SAML provider" page, select Custom SAML 2.0 and click Configure.
Copy the SSO URL information from the Duo Access Gateway admin console Metadata display and paste it into the Slack SAML 2.0 Endpoint (HTTP) field.
Copy the Entity ID information from the Duo Access Gateway admin console Metadata display and paste it into Slack's Identity Provider Issuer field.
The "Public Certificate" is the text of the DAG Metadata certificate supplied by Duo Access Gateway. Open the dag.crt file in a text editor (like Notepad), and copy the entire contents of the file (including the
-----BEGIN CERTIFICATE----- and
-----END CERTIFICATE----- lines). Paste the certificate file text into this field.
Click Expand next to "Advanced Options". New options will appear.
Next to Service Provider Issuer type https://slack.com/ into the field.
Select which team members must use SSO authentication and configure other options under "Settings".
After you've entered all the required information click Save Configuration and Send Binding Emails. This automatically redirects you to the Duo Access Gateway to bind your Slack account to your SSO account. This action also sends an email to your Slack team users with the unique links used to bind their Slack accounts with their SSO accounts.
See the Slack Help Center for more information about SSO binding emails.
Successful completion of your Slack and SSO account binding redirects you back to the Slack Team Settings page.
Learn more about Slack SSO at the Slack Help Center.
You can log on to Slack using your team login page e.g. https://teamname.slack.com. Clicking the Sign in with SAML button redirects you to the Duo Access Gateway login page. Enter your primary directory logon information, approve Duo two-factor authentication, and get redirected back to the Slack site after authenticating.
Congratulations! Your Slack users now authenticate using Duo Access Gateway.
If you plan to permit use of WebAuthn authentication methods (security keys, U2F tokens, or Touch ID) in the traditional Duo Prompt, Duo recommends configuring allowed hostnames for this application and any others that show the inline Duo Prompt before onboarding your end-users.
The Duo Universal Prompt has built-in protection from unauthorized domains so this setting does not apply.
Microsoft's Active Directory Federation Services (AD FS) is a popular choice for SSO because it easily integrates with the AD identity store many organizations already have deployed. Duo's support for cloud applications and SSO drops in to an existing AD FS installation to provide secondary authentication after a user passes primary authentication (successful Active Directory logon).
If you don't already have AD federation running the first step is to install and configure Microsoft AD FS in your organization. Deployment Guides for AD FS versions 2.1, and 3.0/4.0 are available from Microsoft.
Once your AD FS services are up and running, the second step is to configure the SSO partnership between your AD FS service and the external cloud resource, in this case Slack. Learn more about configuring Slack SSO with AD FS at the Slack Help Center.
After you have successfully configured and tested AD FS SSO login to Slack using your AD domain credentials, you can then install the Duo AD FS integration. AD FS protection is included with Duo's paid plans.
With the Duo integration for AD FS installed, users pass primary authentication to the AD FS service as usual. Once primary authentication succeeds, users are forwarded to the Duo service for secondary authentication. After approving logon using one of Duo's authentication methods, the user is fully logged in to Slack.
Using a third-party SSO provider for cloud application access? Duo partners with leading cloud SSO providers like Okta and OneLogin to secure access with our strong and flexible authentication platform.
You can also use Duo two-factor authentication with CAS and Shibboleth on-premises IdPs.
Need some help? Try searching our Knowledge Base articles or Community discussions. For further assistance, contact Support.