What is the easiest way to add SSO to an existing app?

The easiest way is usually to use a hosted identity provider and integrate it with OIDC (OpenID Connect) or SAML, rather than building SSO yourself.

Best practical options

1) Add a hosted auth provider

Use a service like:

• Auth0
• Okta
• Azure AD / Entra ID
• Google Identity / Workspace SSO
• OneLogin
• Clerk / WorkOS for app-focused implementations

These providers handle:

• login UI
• password policies / MFA
• social login
• enterprise SSO
• token issuance
• session management

2) Prefer OpenID Connect if you can

If your app supports it, OIDC is usually the easiest and cleanest option.

• Modern
• Easier than SAML
• Works well for web apps and APIs
• Good library support in most frameworks

Use SAML only if you need to integrate with older enterprise customers or their IdP requires it.

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Easiest implementation path

1. Pick an IdP (Auth0/Okta/Azure AD/etc.)
2. Register your app with it
3. Implement the OIDC login flow
   • redirect user to IdP
   • receive callback
   • validate tokens
   • create local app session
4. Map IdP users to your app users
5. Add logout and session expiration
6. Optionally enable SCIM for automated user provisioning

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If you want the absolute simplest path

If your app is a SaaS product and you want enterprise SSO with minimal work, use:

• WorkOS or Auth0 for enterprise SSO
• OIDC for modern apps
• SAML only when required

WorkOS is especially popular if you want to “add SSO fast” for B2B apps because it abstracts a lot of enterprise-specific complexity.

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Rule of thumb

• Web/mobile app: OIDC
• Enterprise customer requires legacy IdP support: SAML
• Fastest way for B2B SaaS: WorkOS/Auth0/Okta
• Already on Microsoft ecosystem: Azure AD / Entra ID

If you tell me your stack (React, Next.js, Django, Rails, etc.) and whether you need Google/Microsoft login or enterprise SSO, I can suggest the fastest integration path.