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@fastify/cors plugin: preflight hooks, dynamic origin functions, and route-level OPTIONS overrides
Fastify lets you compute Allow-Origin per request—cache expensive database lookups carefully to avoid slowing OPTIONS.
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fastifycorsnodejs
Plugins ecosystem
Order matters: register CORS before routes that attach schemas, or validation may reject OPTIONS bodies.
Multipart plugins can change Content-Type expectations—mirror Allow-Headers for file uploads.
HTTP/2 and HTTP/3
Server push is rarely used with CORS-heavy SPAs—disable push for API subdomains to simplify caches.
QUIC connection migration should not change perceived origin for credentialed requests.