best way to do SSO for SaaS

The best way to do SSO for SaaS is usually:

1) Support OIDC first, SAML second

• OIDC (OpenID Connect) is the modern default:
  • Easier to implement
  • Better developer experience
  • Works well for web apps and APIs
• SAML is still very common in enterprise environments:
  • Many customers will ask for it
  • Often required for legacy IdPs like older Okta/Azure AD setups

Recommendation:
If you’re building SaaS, implement both, but make OIDC your primary path and add SAML for enterprise customers.

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2) Use a dedicated identity provider integration layer

Instead of coding each IdP directly, use a layer/service that handles:

• SAML and OIDC
• metadata/cert rotation
• tenant-to-IdP mapping
• login routing
• user provisioning hooks

Common approaches:

• Build your own abstraction if you have a strong auth team
• Use a provider like Auth0, WorkOS, Clerk, Okta, FusionAuth, Descope, OneLogin, etc.

For most SaaS teams, WorkOS is often a strong fit for enterprise SSO because it simplifies SAML/OIDC and SCIM.

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3) Design for multi-tenant SSO

You’ll want:

• A way to map each customer/org to one or more IdPs
• A login flow like:
  • user enters email
  • you detect the company domain
  • redirect to the right IdP
• Support for:
  • multiple domains per tenant
  • multiple IdPs per tenant if needed
  • fallback to passwordless/password login if SSO isn’t enforced

Important: don’t use email domain alone as your only trust signal until the user is actually authenticated.

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4) Add SCIM for provisioning/deprovisioning

SSO authenticates users, but enterprise customers also want lifecycle management:

• create users automatically
• update attributes/groups
• deactivate users when they leave

SCIM is the standard for that.

If you’re selling to enterprise, SSO + SCIM is the expected combo.

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5) Keep your auth model simple

Best practice:

• Use your app as the source of authorization
• Use SSO only for authentication
• After login, issue your own session/JWT
• Store user and org membership in your own database

Avoid relying on IdP claims for fine-grained authorization beyond basic identity and group sync.

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6) Security essentials

Make sure you have:

• signed assertions / token validation
• strict audience/issuer checks
• certificate rotation handling
• nonce/state validation for OIDC
• logout strategy if needed
• audit logs for login/SSO changes
• MFA support via the customer’s IdP

Also:

• don’t let users switch orgs unless authorized
• protect against account takeover via domain takeover or email aliasing
• verify domain ownership before enabling domain-based auto-routing

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7) Good UX patterns

A good SSO UX usually includes:

• email-first login
• “Continue with SSO” when a domain is recognized
• clear error messages:
  • “No SSO configured for this account”
  • “Your organization uses SSO—please sign in with your company account”
• admin setup flow with IdP metadata upload/config
• test connection button
• ability to disable/enable SSO per tenant

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8) Practical recommendation by company stage

Early-stage SaaS

• Start with OIDC
• Add SAML if an enterprise customer needs it
• Consider using an identity platform rather than building from scratch

Growth-stage SaaS

• Support SAML + OIDC + SCIM
• Add domain discovery and tenant mapping
• Invest in admin self-serve setup

Enterprise SaaS

• Multiple IdPs per tenant
• SCIM
• Just-in-time provisioning
• audit logs
• conditional access / step-up auth support
• dedicated enterprise auth workflows

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If you want the shortest answer:

Use OIDC for modern SSO, add SAML for enterprise compatibility, and pair it with SCIM for provisioning.
For a SaaS product, the easiest and most robust path is usually to integrate with an auth/SSO platform rather than building all IdP integrations yourself.

If you want, I can also give you:

1. a recommended architecture diagram,
2. a build vs buy comparison, or
3. a step-by-step SSO implementation plan for your stack.