Increasingly, scalable distributed applications are being constructed by integrating reusable components spanning multiple administrative domains. Dynamic composition and deployment of such applications enables flexible QoS-aware adaptation to changing client and network characteristics. However, dynamic deployment across multiple administrative domains needs to perform cross-domain authentication and authorization, and satisfy various network and application-level constraints that may only be expressed in terms meaningful within a particular domain.

Our solution to these problems, developed as part of the Partitionable Services Framework, integrates a decentralized trust management and access control system (dRBAC) with a programming and run-time abstraction (object views). dRBAC encodes statements within and across domains using cryptographically signed credentials, providing a unifying and powerful mechanism for cross-domain authorization and expression of network and application constraints. Views de.ne multiple implementations of a reusable component, thus enriching the set of components available for dynamic deployment and enabling fine-grained, customizable access control. We describe the runtime support for views, which consists of a view generator (VIG) and a host-level communication resource (Switchboard) for creating secure channels between pairs of components. We present a simple mail application to illustrate how dRBAC, views, and Switchboard can be used to customize reusable components and securely deploy them in heterogeneous environments.