The rise of the Internet has introduced dramatic changes in managing and sharing digital resources among widely dispersed groups. This paper presents a policy-driven access management approach for ad-hoc collaboration to enable secure information sharing in heterogeneous network environments. In particular, we attempt to incorporate the features of distributed role-based access control, delegation and dissemination control to meet the fundamental access control requirements associated with resource originators. These features are realized in a set of XACML-based Role-based Originator Authorization policies (ROA). We propose a security architecture, called ShareEnabler, to achieve effective authorization and enforcement mechanisms in the context of Peer-to-Peer (P2P) networking oriented file sharing. We briefly discuss our proof-of-concept prototype implementation based on an existing P2P file sharing toolkit developed by Lawrence Berkeley National Laboratory.