Collaboration over the Internet depends on the ability of the members of a group to exchange data in a secure yet unobtrusive manner. WebDAVA is a system that allows users to define their own access-control policies to network resources that they control, enabling secure data sharing within an enterprise. Our design allows users to selectively give fine-grain access to their resources without involving their system administrators. We accomplish this by using authorization credentials that define the users? privileges. Our prototype implements a file-sharing service, where users maintain sensitive-information folders and can allow others to access parts of these. Clients interact with the server over HTTP via a Java applet that transparently handles credential management. This mechanism allows users to share information with users not a priori known to the system, enabling administrator-free management. This work was supported by DARPA and NSF under Contracts F39502-99-1-0512-MOD P0001 and CCR-TC-0208972 respectively.