Security Implementation for Node.js Backend and Flutter App

I need a security expert to implement robust security measures for my Node.js backend and Flutter app. The security measures should cover:
- Data encryption: Ensuring that sensitive data is encrypted both at rest and in transit.
- User authentication: Implementing a secure and efficient user authentication system that is suitable for my backend and app. I am open to using the best practices in the industry.
- API security: Protecting my APIs from potential threats and vulnerabilities.

Additionally, for the app specifically, I want to prioritize:
- Secure storage of sensitive data: Implementing secure methods for storing sensitive data within the app.

The ideal candidate for this project should have extensive experience in security implementation for backend and mobile applications, with a deep understanding of Node.js and Flutter. They should also be well-versed in data encryption techniques and user authentication methods. Experience with regular security audits is a plus.

Let me know you price in your bid