[keep-web] Instruct browsers to allow webdav headers in cross-origin requests
Some WebDAV operations (like COPY and MOVE) supply flags/arguments as HTTP request headers (like Destination). In order for a web browser to use these, keep-web has to list them in the Access-Control-Allow-Headers header in its pre-flight response.
Currently keep-web sends
Access-Control-Allow-Headers: Authorization, Content-Type, RangeThe WebDAV request headers should be added:
ref: https://tools.ietf.org/html/rfc4918 section 21.3