Uploads are served from this origin too, so script-src 'self' would run one
that a cache still holds under a script type from before the upload guard.
Application pages now allow each importmap URL up to its asset directory
(relative root and asset host included), the inline importmap by hash, and
the service worker by worker-src.
(cherry picked from commit 2be2227f40)
script-src 'self', object-src 'none' and base-uri 'self', enforced. The
two inline scripts the importmap helper emits are allowed by their
SHA-256, and the origins its URLs point to (a configured asset host, in
any form Rails accepts) are allowed by name. There is no per-request
nonce, so cached pages stay valid.
DISABLE_CONTENT_SECURITY_POLICY=true leaves the policy off, for an
install whose proxy or customization injects scripts.
(cherry picked from commit 562888251e)
Backport: 1.5.2 has no response cache, so the cached-page test is left out.