Cross-Platform App Development

I'm seeking an experienced application developer to create a cross-platform app for both iOS and Android.

Key Requirements:
- Experience in developing apps for both iOS and Android platforms.
- Ability to implement user login and authentication features (email/password or social media).
- Experience in either social media, e-commerce, or productivity apps.

Ideal Skills and Experience:
- Proficiency in React Native or Flutter.
- Strong understanding of UI/UX design principles.
- Background in secure authentication protocols.
- Proven track record with similar projects.

Please provide a portfolio with relevant projects and a brief outline of your approach.