My Flutter-based news app is already live on the Play Store, yet users can no longer see fresh articles because every request to the backend fails with an “invalid_token” response. The problem is clearly on the authentication layer: we rely on OAuth and the app keeps throwing authentication errors the moment it tries to hit the protected /news endpoint. I need you to dive into the current Flutter code, trace the OAuth flow, and find out why the token that is being attached to each request is considered invalid by the server. Whether the bug lives in the way the token is stored, refreshed, or signed, I want the root cause identified and fixed. The API itself is stable; Postman calls with a valid token work fine, so this is a client-side issue. Deliverables • Clean, commented Flutter code with the OAuth logic corrected • A concise changelog highlighting which files/methods were touched • Steps I should take to publish the patched build to the Play Store (I already have the store listing in place) Please be comfortable using common Flutter tools (Dart, Android Studio, VS Code) and Git for version control so I can review your changes easily. Once the fix is confirmed in an internal build, I will roll it out to production.