I need a secure authentication setup for a mobile app and backend API, but I don't want to own token handling if possible.

If you want a secure mobile-app + backend API auth setup and you don’t want to own token handling, the best pattern is usually:

Recommended approach: Use an external Identity Provider (IdP) with OAuth 2.0 / OpenID Connect

Examples:

• Auth0
• AWS Cognito
• Firebase Auth
• Azure AD B2C
• Okta
• Clerk (more app-focused)

Why this fits your goal

• The IdP handles:
  • user sign-in
  • password reset
  • MFA
  • refresh/access token issuance
  • token rotation
  • session management
  • social login / SSO if needed
• Your app/backend only needs to:
  • redirect users to sign in
  • receive tokens or authorization codes
  • validate tokens on the API
  • enforce authorization

This means you’re not building or storing passwords, and you minimize custom token logic.

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Best-practice architecture

Mobile app

Use Authorization Code Flow with PKCE.

This is the standard secure flow for mobile apps:

1. App opens the IdP login page in the system browser.
2. User authenticates.
3. IdP returns an authorization code.
4. App exchanges the code for tokens using PKCE.
5. App stores tokens securely in the OS secure storage:
   • iOS Keychain
   • Android Keystore / EncryptedSharedPreferences

Backend API

Your API should:

• accept access tokens in Authorization: Bearer <token>
• validate the token signature and claims
• check:
  • issuer (iss)
  • audience (aud)
  • expiration (exp)
  • scopes/roles/claims

Important

• The backend should not trust the mobile app.
• The backend should not accept tokens without verifying them.
• The backend should not store user passwords.
• The app should not handle refresh token logic manually if the IdP SDK can do it safely.

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What “not owning token handling” can realistically mean

You can avoid owning:

• token generation
• refresh token rotation
• login UI/password storage
• MFA
• account recovery
• session revocation

You will still usually need to:

• configure token validation in your API
• map identities to your internal user records
• manage app authorization rules

So you can outsource the hard auth plumbing, but your API still needs to verify tokens.

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Strong recommendation for mobile

Avoid:

• Resource Owner Password Credentials flow (username/password directly in app)
• custom JWT minting unless you truly need it
• storing long-lived tokens in insecure app storage

Use:

• PKCE
• system browser (not embedded webviews)
• short-lived access tokens
• refresh tokens only if needed, preferably with rotation

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Secure implementation pattern

1. User logs in via IdP

• Mobile app redirects to provider’s hosted login page.

2. IdP returns tokens

Typically:

• ID token: who the user is
• Access token: what the API can accept
• Refresh token: get new access tokens without logging in again

3. API validates access token

Use provider’s JWKS endpoint to verify JWT signatures.

4. App stores tokens securely

• access token: memory or secure storage depending on usage
• refresh token: secure storage only

5. Refresh automatically

Let the IdP SDK handle refresh if available; otherwise use standard refresh token flow carefully.

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If you want the simplest safe option

Good choice:

Auth0 + OAuth/OIDC + PKCE + JWT validation in your API

Why:

• mature mobile SDKs
• hosted login
• easy social login/MFA
• good docs
• less custom security work

Good alternatives:

• Firebase Auth if your app is Firebase-centric
• Cognito if you’re on AWS and want tighter AWS integration
• Azure AD B2C if you’re in Microsoft ecosystem or need enterprise identity
• Clerk if you want a more developer-friendly app auth layer

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Minimal checklist

• Use an external IdP
• Use OAuth 2.0 Authorization Code + PKCE
• Use system browser login
• Validate JWTs on the API using JWKS
• Store tokens in Keychain/Keystore
• Use short-lived access tokens
• Enable refresh token rotation
• Add MFA if risk warrants it
• Never put client secrets in the mobile app

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If you want, I can give you one of these next:

1. A recommended architecture diagram
2. A step-by-step flow for iOS/Android + API
3. A provider comparison for Auth0 vs Cognito vs Firebase
4. A sample backend JWT validation setup for your stack (Node, Python, Go, .NET, etc.)