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Duo Single Sign-On for Slack

Last Updated: April 27th, 2020

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.

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.

Duo Single Sign-On

Duo Single Sign-On, now in public beta, 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's public beta 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 configure Duo Single Sign-On with a working an authentication source.

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.

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

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.

Microsoft AD FS

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.

Other Identity Partners

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.

Troubleshooting

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