In this paper we propose a solution to secure interoperability between electronic ID management infrastructures enabling the provision of cross-border eServices to mobile citizens. Our proposal considers an interoperability architecture based on a federation of national infrastructures and follows a cooperation based approach which is fully compatible with and respectful of organizational and technical independence of existing national systems. Provision of cross-country services to mobile citizens requires involved national citizen eAuthentication infrastructures (CEIs) to cooperate for establishing the identity of citizens, without interfering with organizational and technical solutions adopted in each CEI. Indeed, for obvious organizational and political reasons, there cannot be a single organization which is responsible for securing the authentication process in its entirety: instead, national organizations must keep full autonomy and responsibility for authenticating accessing cit...