Security has been a major concern in computer sciences for a long time. However, the definition and the enforcement of a complete security policy are difficult tasks, requiring deep knowledge of the inner workings of the security mechanisms. The management of the security is even more complex in a system such as a Cloud, which is a heterogeneous environment, with multiple applications and tenants. Nowadays, systems, and especially Cloud environments, need a simple way to express the security requirements and to enforce them. This paper describes a new solution that eases the management of the security mechanisms. The solution supports high-level security requirements that are enforced through distributed security properties. Enforcement agents are located on the heterogeneous and distributed nodes. They manage the distributed security properties and configure the heterogeneous security mechanisms. Our solution guarantees global security properties by enforcing consistent distributed properties in an autonomous manner. The autonomous agents dynamically discover the capabilities of the available security mechanisms and compute their configuration. The solution is especially appropriate to secure Clouds, viewed as autonomous distributed environments.