Finalize MERN Stack SSO Integration

I need a professional developer to finalize an almost completed Single Sign-On system developed with MERN stack.

This task will require:
- Proficient understanding of MERN stack development
- Experience in SSO system integration
- Focus on web-based platform integration

As the system is nearly complete, I expect efficient work showcasing a good understanding of the existing system, as well as the ability to bring it to completion seamlessly. Adept problem-solving skills will also be needed to address any potential security or functionality issues left by the previous team.