Public administrations across Europe have been actively following and adopting cloud paradigms at various degrees. By establishing modern data centers and consolidating their infrastructures, many organizations already benefit from a range of cloud advantages. However, there is a growing need to further support the consolidation and sharing of resources across different public entities. The ever increasing volume of processed data and diversity of organizational interactions stress this need even further, calling for the integration on the levels of infrastructure, data and services. This is currently hindered by strict requirements in the field of data security and privacy. In this paper, we present ongoing work aimed at enabling secure private cloud federations for public administrations, performed in the scope of the SUNFISH H2020 project. We focus on architectural components and processes that establish cross-organizational enforcement of data security policies in mixed and heterogeneous environments. Our proposal introduces proactive restriction of data flows in federated environments by integrating real-time based security policy enforcement and its post-execution conformance verification. The goal of this framework is to enable secure service integration and data exchange in cross-entity contexts by inspecting data flows and assuring their conformance with security policies, both on organizational and federation level
