Do I need a separate auth service for enterprise SSO?

Not necessarily.

If you mean enterprise SSO via SAML/OIDC to Okta, Azure AD, Google Workspace, etc., you usually do not need a completely separate auth service. You can often handle it in your existing backend or identity layer.

You typically need:

• An IdP integration (SAML or OIDC)
• User/session management in your app
• Authorization logic for roles, groups, tenants, etc.

You might want a separate auth service if:

• You have multiple apps that should share login/session logic
• You need to support many enterprise customers with different SSO configs
• You want centralized handling of:
  • SAML/OIDC metadata
  • Just-in-time user provisioning
  • SCIM provisioning/deprovisioning
  • Role/group mapping
  • Multi-tenant auth policies
• You want to reduce complexity in each product service

Common patterns

1. Built into your app/backend
   Good for simpler products or one main app.

2. Dedicated auth service / identity broker
   Useful when SSO is a core platform capability.

3. Use a managed identity provider
   Auth0, Okta, Cognito, Clerk, FusionAuth, Azure AD B2C, etc. can save a lot of time.

Rule of thumb

• One app, a few SSO customers → no separate auth service needed.
• SaaS platform, many enterprise tenants, multiple apps → a separate auth layer/service is often worth it.

If you want, I can sketch a reference architecture for SAML/OIDC enterprise SSO in a multi-tenant SaaS.