REST (or Representational State Transfer) is an architectural style first described in Roy Fielding's Ph.D. dissertation on Architectural Styles and the Design of Network-based Software Architectures.
Non-public REST services must perform access control at each API endpoint. Web services in monolithic applications implement this by means of user authentication, authorization logic, and session management. This has several drawbacks for modern architectures which compose multiple microservices following the RESTful style.