Allow custom headers for each object
GCS only allows setting a limited set of headers (Content-Type, Content-Encoding, Cache-Control, etc.). It's missing the ability to set headers like Service-Worker-Allowed, Strict-Transport-Security, X-XSS-Protection, X-Content-Type-Options and Content-Security-Policy. Ideally any header could be set on a per-object basis.
See also https://issuetracker.google.com/issues/36427250 (currently 72 stars).