I’m building a SaaS app and need users to sign in with Google and Microsoft — what auth approach should I use?

For a SaaS app where users need to sign in with Google and Microsoft, the usual best choice is:

Use OpenID Connect (OIDC) / OAuth 2.0 with a dedicated auth layer

In practice, that means one of these approaches:

Best overall for most SaaS apps

Use a managed auth provider that supports Google + Microsoft social/enterprise login, such as:

• Auth0
• Clerk
• WorkOS
• Firebase Auth
• Supabase Auth
• AWS Cognito

This gives you:

• One consistent login flow
• Less security/PKCE/session/token handling to implement yourself
• Easier account linking across providers
• Better support for MFA, passwordless, user management, and enterprise features later

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Recommended auth pattern

1) Use OIDC for login, not plain OAuth

• OAuth 2.0 is for authorization
• OpenID Connect adds identity/login on top of OAuth
• Google and Microsoft both support OIDC

2) Use the Authorization Code Flow with PKCE

This is the current recommended flow for:

• Web apps
• SPAs
• Mobile apps
• Backend-for-frontend architectures

Avoid older flows like the implicit flow.

3) Let your backend create your own app session

After Google/Microsoft authenticate the user:

• Verify the ID token / auth code server-side
• Map them to your internal user record
• Create your own session cookie or JWT for your app

This keeps your app independent from Google/Microsoft token lifetimes.

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If you want the simplest architecture

Option A: Managed auth provider

Best if you want to move fast and avoid auth complexity.

Typical flow:

1. User clicks “Sign in with Google” or “Microsoft”
2. Redirect to provider
3. Provider returns user identity to your auth service
4. Your app creates a session

Good when:

• You want to ship quickly
• You may need SSO/SAML later
• You want account linking and profile sync handled for you

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If you want to build it yourself

Option B: Direct integration with Google + Microsoft using OIDC

Do this only if you’re comfortable owning:

• PKCE
• Token validation
• Refresh token handling
• Account linking
• Session security
• Redirect URI management
• CSRF/state handling

This can work well, but it’s more maintenance.

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SaaS-specific recommendation

If you’re building a B2B SaaS, consider:

• Google login
• Microsoft login
• Potentially SAML SSO later for enterprise customers

In that case, a provider like WorkOS or Auth0 is often a strong fit because they handle both:

• Social login
• Enterprise SSO

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Security checklist

No matter which route you choose:

• Use Authorization Code + PKCE
• Validate issuer, audience, signature, nonce, and expiration
• Use HTTPS only
• Store sessions in HttpOnly, Secure cookies if web-based
• Support account linking carefully to avoid duplicate users
• Don’t trust email alone as a unique identity without verification rules

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My practical recommendation

For most SaaS startups:

• Use Auth0 / Clerk / WorkOS / Supabase Auth
• Enable Google + Microsoft
• Use OIDC Authorization Code Flow with PKCE
• Create your own app session after login

If you’re enterprise-focused:

• Pick WorkOS or Auth0
• Plan for SAML + SCIM in addition to Google/Microsoft

If you want, I can also recommend the best option based on your stack:

• Next.js / React
• Django / FastAPI
• Rails
• Node / Express
• Go
• Mobile app