Cross-Platform Mobile App Development

I'm looking for an experienced mobile app developer to create an application for both iOS and Android platforms. The app will require user authentication features.

Key Requirements:
- Cross-platform development expertise
- Experience in implementing user authentication
- E-commerce, Social Media, or Utility/Tools app experience is a plus

Ideal Skills:
- Proficiency in React Native or Flutter
- Strong knowledge of security protocols for user data
- UI/UX design capabilities

Please share relevant experience and portfolio.