In this paper we describe the STORK Large Scale Pilot (LSP). STORK has been a project driven by eighteen European Union (EU) and European Economic Area (EEA) Member States (MS). The objective was to develop an interoperability framework to enable cross-border use of national electronic identity (eID) solutions. The framework has been tested in six pilots that involved MS and European Commission production environments. The paper describes the technical STORK solution that supports eID federation both in centralized and in decentralized deployment models. We refer to these as Pan-European Proxy Service (PEPS) for centralized deployment, as middleware (MW) for the decentralized deployment, respectively. The paper puts particular attention to security and privacy aspects.