Developing Facebook Login Authentication
Facebook Login in mobile apps is a working method but with a reputation issue. Users decline due to Meta ecosystem fatigue, iOS 14+ App Tracking Transparency reduced data Meta gets. Still, for apps targeting 25-45 age audience with global reach, Facebook Login shows good conversion.
Technical Integration
Meta SDK: pod 'FacebookLogin' (iOS) / implementation 'com.facebook.android:facebook-login:latest' (Android). SDK is substantial — adds ~4-8 MB to binary. If binary size is critical — alternative: OAuth2 PKCE flow in browser without Meta SDK, but then lose native experience.
On iOS: add FacebookAppID, FacebookDisplayName to Info.plist, URL Scheme fb{app_id}. AppDelegate or SceneDelegate must pass application(_:open:options:) to ApplicationDelegate.shared.
On Android: meta-data in AndroidManifest.xml, queries setup for Intent to Facebook app. With Android 11+ without queries element, Facebook app not discoverable.
Permissions and Graph API
At login, request only needed permissions. Minimum: ["public_profile", "email"]. public_profile gives name and avatar. email — address, but Facebook doesn't guarantee verification: user might have entered invalid email. email can be null if user hid it in Facebook settings.
After getting accessToken — request to Graph API for data:
GET graph.facebook.com/me?fields=id,name,email,picture.type(large)&access_token=TOKEN
id in Graph API — stable user identifier for your app (App-Scoped ID). Different apps see different id for same user — intentional Meta isolation.
Backend verifies accessToken via GET graph.facebook.com/debug_token?input_token=TOKEN&access_token=APP_TOKEN. Checks token issued for your app_id and not expired.
Typical gotcha: on iOS with Facebook SDK, if Facebook app installed on device — login via Facebook app (fast login), if not — via Safari. Behavior different, need to test both scenarios.
Timeline: 5-8 working days. Includes iOS + Android integration, server token verification via Graph API, handling missing email, testing with/without Facebook app on device.