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Duo Single Sign-On for Slack

Last Updated: October 23rd, 2020

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.

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

  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

Duo's next-generation authentication experience, the Universal Prompt, is coming to web-based applications that display the current Duo Prompt in browsers.

Migration to Universal Prompt for your Slack application is a two-step process:

  • Update the Slack application to support the Universal Prompt.
  • Enable the Universal Prompt experience for users of that Slack application (when the Universal Prompt becomes available)

We've already updated the Duo Slack application to support the Universal Prompt when it's ready, so there's no action required on your part to update. The "Universal Prompt" section of this application's details page in the Admin Panel reflects this status today as "New Prompt Ready".

Universal Prompt Info - Application Updated

When the Universal Prompt becomes available, you'll return here to activate it for users of this application.

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.

Read the Universal Prompt Update Guide for more information about the update process to support the new prompt, and watch the Duo Blog for future updates about the Duo Universal Prompt.

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. Enter your primary directory logon information, approve Duo two-factor authentication, and get redirected back to the Slack site after authenticating.

Duo Single Sign-On Login and Authentication Prompt

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.