Access control is an important security issue. It has been addressed since the late 1960s in the early time-sharing computer systems. Many access control models have been proposed since than but of particular interest is Ferraiolo and Khun's role-based access control model (RBAC). It is a simple and yet general model which has been deeply studied and applied both in industry and in academia. A variety of industrial standards have been proposed based on this model. Generating code for an access control policy is an interesting challenge. Understanding access control as a non-functional concern that cross-cuts the functional part of a system raises difficulties quite suitable for a solution based on aspect-oriented programming. In this paper, we address the problems of specification and validation of code generation for access control policies targeting an aspect-based infra-structure. We propose an MDA approach. The code generator is a transformation from SecureUML, an RBAC-based modeling language, to the language Aspects for Access Control (AAC), an aspect-oriented modeling language proposed in this paper. Metamodels are used to represent the languages and to specify the transformation. A metamodel is used to represent the abstract syntax of a language and the constraints that a given instance model of the metamodel must fulfill. We also use a metamodel to specify the code generator. This transformation metamodel, together with all the constraints, that is, from both languages and those constraints regarding the merge of the two languages, we call a transformation contract. It merges and conservatively extends the source and target metamodels of the model transformation it represents. In the context of code-generation for access control policies, the transformation contract specifies the relationships between the abstract syntaxes of SecureUML and AAC and constrains the two languages. The validation of the code generator also uses the transformation contract. For a given access control policy and aspect, represented as instances of the appropriate metamodels, with aspects produced by the code generator, the constraints of the transformation contract must hold. We have prototyped a transformer from SecureUML to aspects on top of ITP/OCL, an OCL interpreter that automatically validates the generated aspect code by applying the constraints of the transformation contract.
