Prohibiting unauthorized access to critical resources and data has become a major requirement for enterprises. Access control (AC) mechanisms manage requests from users to access system resources; the access is granted or denied based on authorization policies defined within the enterprise. One of the most used AC paradigms is role-based access control (RBAC). In RBAC, access rights are determined based on the user's role, e.g., her job or function in the enterprise.Many different types of RBAC authorization policies have been proposed in the literature, each one accompanied by the corresponding extension of the original RBAC model. However, there is no unified framework that can be used to define all these types of RBAC policies in a coherent way, using a common model. Moreover, these types of policies and their corresponding models are scattered across multiple sources and sometimes the concepts are expressed ambiguously. This situation makes it difficult for researchers to understand the state of the art in a coherent manner; furthermore, practitioners may experience severe difficulties when selecting the relevant types of policies to be implemented in their systems based on the available information. There is clearly a need for organizing the various types of RBAC policies systematically, based on a unified framework, and to formalize them to enable their operationalization.In this paper we propose a model-driven engineering (MDE) approach, based on UML and the Object Constraint Language (OCL), to enable the precise specification and verification of such policies. More specifically, we first present a taxonomy of the various types of RBAC authorization policies proposed in the literature. We also propose the GemRBAC model, a generalized model for RBAC that includes all the entities required to define the classified policies. This model is a conceptual model that can also serve as data model to operationalize data collection and verification. Lastly, we formalize the classified RBAC policies as OCL constraints on the GemRBAC model. To facilitate such operationalization, we make publicly available online the Ecore version of the GemRBAC model and the OCL constraints corresponding to the classified RBAC policies.

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A Role-based Access Control (RBAC) mechanism prevents unauthorized users to perform an operation, according to authorization policies which are defined on the user's role within an enterprise. Several models have been proposed to specify complex RBAC policies. However, existing approaches for policy enforcement do not fully support all the types of policies that can be expressed in these models, which hinders their adoption among practitioners.In this paper we propose a model-driven enforcement framework for complex policies captured by GemRBAC+CTX, a comprehensive RBAC model proposed in the literature. We reduce the problem of making an access decision to checking whether a system state (from an RBAC point of view), expressed as an instance of the Gem-RBAC+CTX model, satisfies the constraints corresponding to the RBAC policies to be enforced at run time. We provide enforcement algorithms for various types of access requests and events, and a prototype tool (MORRO) implementing them. We also show how to integrate MORRO into an industrial Web application. The evaluation results show the applicability of our approach on a industrial system and its scalability with respect to the various parameters characterizing an AC configuration. CCS CONCEPTS• Security and privacy → Access control; • Software and its engineering → Model-driven software engineering; KEYWORDS role-based access control, enforcement, policies, model-driven engineering ACM Reference Format:

A role-based access control (RBAC) policy restricts a user to perform operations based on her role within an organization. Several RBAC models have been proposed to represent different types of RBAC policies. However, the expressiveness of these models has not been matched by specification languages for RBAC policies. Indeed, existing policy specification languages do not support all the types of RBAC policies defined in the literature.In this paper we aim to bridge the gap between highlyexpressive RBAC models and policy specification languages, by presenting GemRBAC-DSL, a new specification language designed on top of an existing, generalized conceptual model for RBAC. The language sports a syntax close to natural language, to encourage its adoption among practitioners. We also define semantic checks to detect conflicts and inconsistencies among the policies written in a GemRBAC-DSL specification. We show how the semantics of GemRBAC-DSL can be expressed in terms of an existing formalization of RBAC policies as OCL (Object Constraint Language) constraints on the corresponding RBAC conceptual model. This formalization paves the way to define a modeldriven approach for the enforcement of policies written in GemRBAC-DSL.