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Duo Single Sign-On for Slack

Last Updated: August 26th, 2021

Add two-factor authentication and flexible security policies to Slack SSO logins with Duo Single-Sign On, our cloud-hosted SAML 2.0 identity provider, complete with inline self-service enrollment and Duo Prompt.

Duo Federal customers or those looking for an on-premises SSO solution: try Duo Protection for Slack with Duo Access Gateway.

Overview

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.

About Duo Single Sign-On

Duo Single Sign-On is our cloud-hosted SSO product which 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 Single Sign-On acts as an identity provider (IdP), authenticating your users using existing on-premises Active Directory (AD) or any SAML 2.0 IdP and prompting for two-factor authentication before permitting access to Slack.

Duo Single Sign-On is available in Duo Beyond, Duo Access, and Duo MFA 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.

Configure Single Sign-On

Before configuring Slack you'll first need to enable Duo Single Sign-On for your Duo account and configure a working authentication source.

Once you have your SSO authentication source working, continue to the next step of creating the Slack application in Duo.

Create the Slack Application in Duo

  1. Log on to the Duo Admin Panel and navigate to Applications.

  2. Click Protect an Application and locate the entry for Slack with a protection type of "2FA with SSO hosted by Duo (Single Sign-On)" 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. You'll need the information on the Slack page under Metadata later.

  3. The Slack subdomain is the unique subdomain used when logging into your company's Slack site. For example, if your Slack login URL is https://example.slack.com, enter example as the subdomain.

  4. Check the box next to Enterprise Grid if your Slack plan is Enterprise Grid.

  5. Slack uses the Mail attribute, Username attribute, First name attribute, and Last name attribute when authenticating. We've mapped the bridge attributes to Duo Single Sign-On supported authentication source attributes as follows:

    Bridge Attribute Active Directory SAML IdP
    <Email Address> mail Email
    <Username> sAMAccountName Username
    <First Name> givenName FirstName
    <Last Name> sn LastName

    If you are using non-standard attributes for your authentication source, check the Custom attributes box and enter the name of the attributes you wish to use instead.

    Duo Slack Application Settings

  6. 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.

  7. Scroll to the bottom of the page and click the Save button.

Duo Universal Prompt

The new Universal Prompt provides a simplified and accessible Duo login experience for web-based applications, offering a redesigned visual interface with security and usability enhancements.

Universal Prompt Traditional Prompt
 Duo Push in Universal Prompt  Duo Push in Traditional Prompt

We've already updated the Duo Slack application hosted in Duo's service to support the Universal Prompt, so there's no action required on your part to update the application itself. You can activate the Universal Prompt experience for users of new and existing Duo Slack applications from the Duo Admin Panel.

Before you activate the Universal Prompt for your application, it's a good idea to read the Universal Prompt Update Guide for more information about the update process and the new login experience for users.

Activate Universal Prompt

Activation of the Universal Prompt is a per-application change. Activating it for one application does not change the login experience for your other Duo applications.

The "Universal Prompt" area of the application details page shows that this application is "New Prompt Ready", with these activation control options:

  • Show traditional prompt: (Default) Your users experience Duo's traditional prompt when logging in to this application.
  • Show new Universal Prompt: Your users experience the Universal Prompt when logging in to this application.

Universal Prompt Info - Application Ready for Universal Prompt

Enable the Universal Prompt experience by selecting Show new Universal Prompt, and then scrolling to the bottom of the page to click Save.

Once you activate the Universal Prompt, the application's Universal Prompt status shows "Update Complete" here and on the Universal Prompt Update Progress report.

Universal Prompt Info - Universal Prompt Activation Complete

Should you ever want to roll back to the traditional prompt, you can return to this setting and change it back to Show traditional prompt.

Universal Update Progress

Click the See Update Progress link to view the Universal Prompt Update Progress report. This report shows the update availability and migration progress for all your Duo applications in-scope for Universal Prompt support. You can also activate the new prompt experience for multiple supported applications from the report page instead of visiting the individual details pages for each application.

Enable Slack SSO

Add Duo Single Sign-On as a new single sign-on provider in Slack.

  1. Log on your Slack administrative site. On the sidebar menu navigate to AdministrationAuthentication. Click the Configure link for "SAML authentication".

  2. Copy the SAML 2.0 Endpoint (HTTP) from the Duo Admin Panel Metadata section and paste it into the Slack SAML 2.0 Endpoint (HTTP) field.

    Example: https://sso-abc1def2.sso.duosecurity.com/saml2/sp/DIABC123678901234567/sso

  3. Copy the Identity Provider Issuer from the Duo Admin Panel Metadata section and paste it into Slack's Identity Provider Issuer field.

    Example: https://sso-abc1def2.sso.duosecurity.com/saml2/sp/DIABC123678901234567/metadata

  4. Click Download certificate next to "Public Certificate" on the Duo Admin Panel under Downloads to download the Duo Single Sign-On signing certificate. Open the certificate 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 the Public Certificate field in Slack.

    Slack Single Sign-On Setting Edit

  5. Select which team members must use SSO authentication and configure other options under "Settings".

  6. After you've entered all the required information click Save Configuration. This automatically redirects you to Duo Single Sign-On 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.

  7. 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.

Using SSO

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 Single Sign-On login page to enter your primary directory logon information. For example, this is the SSO login page when your authentication source is Active Directory.

Duo Single Sign-On Login and Authentication Prompt

Successful verification of your primary credentials redirects you to Duo. Complete Duo two-factor authentication when prompted and then you'll return to Slack to complete the login process.

OIDC Duo Prompt *Universal Prompt experience shown.

You can also log into Slack using Duo Central, our cloud-hosted portal which allows users to access all of their applications in one spot. Link to Slack in Duo Central by adding it as an application tile. Once the tile has been added, log into Duo Central and click the tile for Slack.

Congratulations! Your Slack users now authenticate using Duo Single Sign-On.

Enable Remembered Devices

To minimize additional Duo two-factor prompts when switching between Slack and your other Duo Single Sign-On SAML applications, be sure to apply a shared "Remembered Devices" policy to your SAML applications.

Troubleshooting

Need some help? Try searching our Knowledge Base articles or Community discussions. For further assistance, contact Support.