Android App with User Login

I need an Android application built from the ground up. The core requirement is a smooth, secure user-login flow (email, phone, or social sign-in is fine as long as it is robust and well-documented). This is strictly an application-development job—no marketing or web work. My goal is to monetize the app later, so the code must be clean, scalable, and ready for future features such as in-app payments or push notifications. Key expectations • Android-native code (Kotlin or Java) that follows current Material guidelines • Clear separation between front-end, authentication logic, and any backend you choose (Firebase, Supabase, or a lightweight custom API) • Complete source code, build instructions, and a signed release APK/Bundle Once login is working flawlessly and passes basic penetration tests, we can discuss adding revenue features in a follow-up milestone. I’m ready to move quickly and will respond promptly to questions.