Required C#,C++,Internet of Things,RFID freelancer for Technical Architecture of Simple but Robust NFC Access Terminal job

Help me clear out specifications for building a simple and custom access control/terminal reader solving my needs. My requirements are the following:
1) An end-user should be able to open an app on his smartphone and put it in reach of the terminal where the terminal should then validate the user with NFC or something.
2) If validated positively, then the access terminal should open the turnstile and allow entry to the end-user.

IMPORTANT: I'm not looking for someone to create a mobile application, I'm looking for someone who can help me DESIGN and create/architecture the access control system flow.

Skills & Expertise Required

C# C++ Internet of Things RFID