Accessing remote resource is a principal challenge of grid computing. For wide-area file sharing, a most difficult problem is the inability to access files distributed in different administrative domains. In this paper, we propose a file system architecture called VegaFS, which is detached from administrative domains entirely and provides cross-domain file access abilities. The main idea is to adopt public keys in native file systems and transfer the management work of administrator to trusted certificate authorities (CAs). Compared with other systems, VegaFS provides several benefits, such as grid-wide unique user identities, cross-domain file access capability, scalabilities, fine-grained dynamic access control and better securities.