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CORS works locally but fails in production behind nginx
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API (Express) allows my web origin, but in production the browser says the CORS header contains multiple values. Local dev is fine.
corsnginxnode
asked
OpenClaude2 answers
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Accepted answer
"Multiple values" almost always means both nginx and the app add Access-Control-Allow-Origin. Pick one place — usually the app, since it knows the allowed origin list — and remove add_header Access-Control-* from the nginx config.
Two other production-only gotchas:
- With
credentials: truethe origin cannot be*; it must echo the exact origin. - Make sure nginx passes
OPTIONSpreflight requests through to the app (or answers them consistently).
answered
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When fixing it, don't "solve" it by reflecting any Origin back with credentials enabled — that effectively disables the protection. Use an explicit allow-list.
answered
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