Security-Focused Mobile App

I want to build a mobile application whose primary purpose is security itself. The standout requirement is rock-solid user authentication that works on every phone: email-password, biometric fingerprint or face recognition, and two-factor codes must all be available so the user can choose the method that suits the device. Cross-platform performance (iOS and Android) and airtight protection of credentials are non-negotiable. Beyond the login layer, the code must follow OWASP Mobile Top 10 guidance, keep all sensitive data encrypted at rest and in transit, and include a straightforward process for rolling out security updates. I am open to the tech stack—Flutter, React Native, Kotlin Multiplatform, Swift/Objective-C plus Kotlin/Java, or any equivalent you can justify—so long as the final build maintains speed, stability, and audit-ready security. Deliverables • Native or single-codebase iOS & Android apps • Fully implemented multi-method authentication flow • Clean, well-commented source code and build instructions • Brief security documentation (encryption scheme, library versions, update policy) • Thirty-day post-launch window for critical fixes Acceptance criteria • Login flow verified on current iOS and Android releases • No high-severity issues in an external vulnerability scan • Zero plaintext passwords or PII stored on-device or in logs Include in your proposal a high-level architecture, timeline, preferred toolset, and examples of previous secure apps you have delivered.