Phase 14.A, both halves of it in one middleware wrapped around the whole
router — outside requireAuth, so POST /login and POST /setup/{token} are
covered too.
Headers: CSP, X-Content-Type-Options, X-Frame-Options, Referrer-Policy, and
HSTS only where the deployment is HTTPS-only (the same CookieSecure condition
that gates the cookie's Secure attribute; on the plain-HTTP dev instance HSTS
would pin the browser to a scheme that instance does not speak). HSTS goes
without includeSubDomains on purpose: the panel may sit at an apex, and
forcing HTTPS on every unrelated subdomain of the operator's domain for a year
is not this project's call. They are emitted here rather than delegated to the
reverse proxy, so the part that is easy to get wrong lives in the service.
Origin check: this is what SameSite=Lax cannot do. SameSite is judged per site
(registrable domain), so a neighbouring host — a CMS, a forgotten staging
subdomain — is same-site and its forged POST arrives with the session cookie
attached. Sec-Fetch-Site and Origin are judged per origin and tell it apart.
For the typical deployment, where the panel is a subdomain of a domain used
for other things, that neighbour is the realistic attacker, not a theoretical
one; POST /domains/import is the case that turns a blind write into working
credentials on someone else's relay.
A request carrying neither header is still let through — the risk accepted in
the plan, since a client that old cannot be checked at all and the strict mode
would not protect it, only break the panel in it.
The check compares Origin's host against r.Host, not the full origin: the
panel speaks plain HTTP behind the proxy and does not know its own external
scheme. That makes it depend on the proxy preserving Host. All four shipped
fragments do, but one that rewrites it would turn every form submission into a
403, so the rejection logs both sides of the comparison — otherwise the
symptom reads as "the panel stopped saving anything".
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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