Robust authentication and authorization are vital to next-generation distributed medical systems-the Medical Internet of ings (MIoT). However, there is yet no good authorization model for real-time multi-channel data from systems of heterogeneous devices providing multiple physiological parameters for clinicians who may change on a minute-by-minute basis. We present a exible authorization architecture for interoperable medical systems, and an implementation and evaluation in the context of the Medical Device Coordination Framework (MDCF) high-assurance middleware. Our framework is based on the well-studied A ributed Based Access Control model, but we introduce a new method of a ribute inheritance that provides more ne-grained access control, supporting multiple di erent authorization levels for multiple physiological data channels from the same device, and rich and expressive policy speci cation which facilitates plug-and-play connectivity of devices-most do not require pre-speci cation of individual permissions. Our architecture is standards-compliant and modular, using the eXtensible Access Control Markup Language (XACML), and Axiomatics Language for Authorization (ALFA) for policy speci cation, and standalone authorization modules which can be integrated with other platforms such as OpenICE. We stress-test our implementation in a realistic distributed system con guration, and show that the unoptimized system introduces negligible network and storage overhead, and minimal memory and CPU overhead. CCS CONCEPTS •Security and privacy →Access control; Authorization; •Applied computing →Health care information systems; •Computer systems organization →Embedded and cyber-physical systems;

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