Cloud computing is a new concept that has interesting advantages; high computing performances provided as needed, much lower cost than inhouse infrastructures, and better reliability and scalability. However, with some drawbacks that are impeding its adoption, security is so far the most alarming concern for companies or organizations. Access control policies, for example, are the most challenging issue that has been tackled these last years; to ensure that the right user is accessing the right resources in such a distributed, virtual and scalable environment handled by a third party, to manage an access request to a shared resource from heterogeneous entities following different policies. In this study, the authors aim to overcome this issue by implementing an access control architecture enabling access to the shared data for collaborating organizations. They propose a model supplied with an ontology database describing the whole environment to control access to a publish/subscribe messaging protocol; which capitalizes on the advantages provided by innovative techniques such as Semantic Web technologies and the publish/subscribe protocol. Semantic Web technologies provide dynamism and scalability for this model thanks to its SWRL inference engine while the publish/subscribe protocol, in this case, MQTT, which is a light-coupling protocol simplifies the traffic between the different actors involved.