OAuth login not working on mobile app

Here are the most common reasons OAuth login fails in a mobile app, plus a quick checklist to debug it.

Common causes

1. Redirect URI mismatch

   • The redirect URI in the app must exactly match what’s registered in the OAuth provider.
   • Common issues: wrong scheme, missing path, trailing slash, http vs https.

2. Deep link / app link not configured

   • Mobile apps usually need custom URL schemes or universal/app links.
   • If the browser can’t hand control back to the app, the login flow breaks.

3. Wrong client type or client ID

   • Mobile apps should use a client configured for native/mobile use.
   • Using a web client ID in a native app can fail.

4. PKCE missing or incorrect

   • Many providers require PKCE for mobile OAuth.
   • If the code verifier/challenge isn’t handled correctly, token exchange fails.

5. Browser / webview issues

   • Some providers block login inside embedded webviews.
   • Use system browser flows when required.

6. Callback not handled in app

   • The app may receive the redirect but not process it.
   • Check app routing, intent filters, and callback code.

7. App signing / package name mismatch

   • Some providers verify package name, SHA-1/SHA-256, bundle ID, or team ID.

8. Network or CORS-like restrictions

   • Less common in native apps, but proxy/VPN/firewall issues can interrupt the flow.

Quick checklist

• Verify the redirect URI is identical everywhere.
• Confirm the app has the right URL scheme / intent filter / universal link.
• Use the correct native/mobile OAuth client ID.
• Ensure PKCE is enabled and implemented.
• Test using the system browser instead of an embedded webview.
• Check logs for:
  • authorization error
  • token exchange error
  • redirect not received
• Confirm provider settings:
  • package name / bundle ID
  • signing fingerprint
  • allowed callback URLs

Best next step

If you share:

• platform: iOS / Android / Flutter / React Native / Expo
• OAuth provider: Google / Auth0 / Azure AD / Cognito / etc.
• exact error message or log
• redirect URI you’re using

…I can help pinpoint the issue quickly.