CORS and CDNs: Cache Rules, Headers, and Gotchas
CORS gets weird fast once a CDN sits in front of your app. Without a CDN, you mostly think about browser rules: Origin, preflights, Access-Control-Allow-Origin, maybe credentials. Add a CDN and now you also have cache keys, header normalization, OPTIONS caching, stale variants, and the classic bug where one origin gets cached and leaked to another. I’ve seen teams debug this for hours because the app server was “correct” but the CDN was serving the wrong cached CORS headers. ...