Auth0 + Slack integration
Set up Auth0 as the identity provider for Slack via SAML — enabling Auth0 (often via Auth0 CIC for B2B Organizations) to sign in to Slack.
- Auth0 tenant admin
- Slack workspace owner
1. Create a new SAML 2.0 application in Auth0
In the Auth0 admin console, create a new SAML 2.0 application. Choose "Web Application" type. Note the placeholders for ACS URL + Entity ID — you'll get these from Slack in step 3.
2. Get the SAML metadata URL from Auth0
Auth0 exposes the IdP metadata at a stable URL. Copy this URL — you'll paste it into Slack's SSO configuration. Alternatively, download the metadata XML if Slack doesn't support URL-based metadata.
3. Configure SSO in Slack
In Slack's admin → security → SSO settings, paste the Auth0 metadata URL (or upload the XML). Slack will display the ACS URL + Entity ID it expects — copy these.
4. Return to Auth0 + complete the SAML app config
Paste Slack's ACS URL into the Auth0 app's Single Sign-On URL field. Paste the Entity ID into the Audience URI field. Set the NameID format to EmailAddress (or persistent if Slack expects that).
5. Configure attribute mapping
Map the attributes the SP expects (see the Attribute Mapping section below). At minimum, email is required. Most apps also expect firstName + lastName.
6. Assign users + groups
In Auth0, assign the SAML app to users or groups that should have access. Test with a pilot group before broad rollout.
7. Test end-to-end
Sign in to Slack via the IdP-initiated link (from Auth0 dashboard) AND via SP-initiated (direct Slack login URL). Both should work. Check the SAML Tracer browser extension or SAML decoder to inspect the assertion if anything fails.
What flows from where.
| Source (Auth0) | Target (Slack) | Note |
|---|---|---|
| user.email | NameID | — |
| user.email | — | |
| user.given_name | givenName | — |
| user.family_name | familyName | — |
- Clock skew: Auth0 and Slack clocks must be within ~5 minutes. NTP-sync both. SAML's NotBefore + NotOnOrAfter are strict.
- NameID format mismatches are the most common failure. Slack typically wants EmailAddress; Auth0 defaults vary. Mismatch → cryptic "invalid assertion" errors.
- Just-in-time (JIT) provisioning vs SCIM: many apps support both. SAML JIT creates the user on first SSO; SCIM creates them ahead of time. Pick one — both can cause attribute drift.
- Audience restriction: Slack's expected Audience URI must match exactly what the IdP sends. Trailing slashes + protocol (http vs https) matter.
- Signed Response vs signed Assertion: many SPs require the Assertion to be signed (not just the Response envelope). Check the SP's docs.
- For B2B SaaS: this lets your customers federate their Auth0 tenant into Slack. The customer manages users in Auth0; Slack trusts the federation.
- IdP-initiated SSO works (sign in from the IdP dashboard)
- SP-initiated SSO works (visit Slack directly + get redirected to IdP)
- User attributes flow through correctly (email, name, groups)
- Logout (single logout if supported) works as expected
- Step-up MFA fires when policy requires it
- Unauthorized users (not assigned to the app) get a clean denied message
- Capture a successful SAML response and inspect it (use the SAML decoder tool)
For the latest vendor-side configuration changes, refer to:
Slack SAML SSO + Auth0 →