RdaFileExplorer runs under the account associated with the ApplicationPool set to the application. This means that you can change the permission for the whole application, and cannot set specific permission for the ContentProvider. In your case you can expose the shared drive through FTP with a specific permissions (setup authentication) and then use the FTPContentProvider
(it accepts credentials for the FTP server) in order to read and write to the shared drive (through FTP server).
All the best,
the Telerik team