In the SECREDAS project, the car-sharing system embodies one of the laboratory demonstrators (pilots). The system consists of an embedded device for car access, a backend server, and a mobile app. In addition, the system can be easily adapted to an access control system in general, such as car fleet management. Our team designed, implemented, and validated the system in a laboratory environment, therefore TRL (Technology Readiness Level) 4 was achieved. The implementation was also supported by design patterns developed in the project. Moreover, we addressed the security, safety, and privacy issues. This article reports the progress of work and the results achieved. Key aspects such as Identity management, Representative State Transfer (REST) API (Application Programming Interface), threat assessment and key transfer methods are also described in more detail. In this work, the symmetric rent token (car key) is heavily used; however, other techniques are presented.