Access Control is crucial for security management, but in the context of the Internet of Things it cannot be implemented the same way as traditional systems do. Indeed, devices that make the Internet of Things impose some constraints that encourage the design of new access control mechanisms, which should provide flexibility of configuration, as well as support several authorization scopes at the same time, yet being computationally light, dynamic and scalable in order to be ready for the forthcoming Cloud Computing paradigm. In this paper we propose an authorization model that is based on the OAuth 2.0 protocol. From the point of view of the identity provider, this model allows managing roles and permissions for an application-scoped authorization, to enable more flexible scenarios in which multiple tenants take part. With regard to devices, the OAuth 2.0 makes authorization extremely light, because all the required information is provided with a token. Considering all this, authorization management is completely delegated to an external system, so that an as-a-service access control mechanism is provided. The proposed model complies with the security, flexibility and performance requirements that are needed in the Internet of Things paradigm.

access control is a key element when guaranteeing the security of online services. However, devices that make the Internet of Things have some special requirements that foster new approaches to access control mechanisms. Their low computing capabilities impose limitations that make traditional paradigms not directly applicable to sensors and actuators. In this paper, we propose a dynamic, scalable, IoT-ready model that is based on the OAuth 2.0 protocol and that allows the complete delegation of authorization, so that an as a service access control mechanism is provided. Multiple tenants are also supported by means of application-scoped authorization policies, whose roles and permissions are fine-grained enough to provide the desired flexibility of configuration. Besides, OAuth 2.0 ensures interoperability with the rest of the Internet, yet preserving the computing constraints of IoT devices, because its tokens provide all the necessary information to perform authorization. The proposed model has been fully implemented in an open-source solution and also deeply validated in the scope of FIWARE, a European project with thousands of users, the goal of which is to provide a framework for developing smart applications and services for the future Internet. We provide the details of the deployed infrastructure and offer the analysis of a sample smart city setup that takes advantage of the model. We conclude that the proposed solution enables a new access control as a service paradigm that satisfies the special requirements of IoT devices in terms of performance, scalability and interoperability.