A page on another origin can POST text/plain or a form without a CORS
preflight, so its visitors' browsers could store reports although the
server sends no CORS headers. decodeJSON now refuses a request whose
Content-Type is not application/json (parameters such as charset
allowed), and the report handler answers it 415 with the usual error
body, storing nothing. A JSON POST waits for the preflight, which only
an origin in CORS_ALLOWED_ORIGINS passes; the page already sends
application/json.
Model: opus-5-5
sneak