Cross-Origin Resource Sharing (CORS)
Cross-Origin Resource Sharing (CORS) is a browser security mechanism that controls whether a web page on one origin may read responses from another origin. Servers advertise permitted caller origins and methods using HTTP response headers such as Access-Control-Allow-Origin.
Technical Architecture & Deep-Dive
Browsers enforce the same-origin policy by default, blocking JavaScript from reading cross-origin API responses even when the network request technically succeeds. CORS relaxes this only when the API returns explicit permission headers that match the page origin.
Misconfigured CORS, such as reflecting arbitrary Origin values or using a wildcard with credentials, can expose private data to hostile sites. An edge proxy on your own domain gives browsers a same-origin URL, attaches consistent CORS headers for your frontends, and forwards sanitized requests to third-party APIs that may not support browser callers at all.
Key Architectural Benefits
Implement Cross-Origin Resource Sharing (CORS) at the Edge
Deploy lightweight API aggregation, edge caching, and secret injection in minutes without Docker containers or complex servers.
Frequently Asked Questions
Q:Does CORS protect my API from non-browser clients?
No. CORS is enforced by browsers only. Server-side scripts, mobile apps, and curl ignore CORS headers. Always authenticate and authorize every request.
Q:What is the difference between CORS and CORS preflight?
CORS is the overall cross-origin permission model. Preflight is an OPTIONS request the browser may send first for certain cross-origin calls to confirm those permissions.
Related Architecture Concepts
Cross-Origin Resource Sharing (CORS) is a browser security protocol that restricts web applications from making API requests to a different domain unless the server explicitly grants permission via HTTP headers. Edge proxies resolve CORS errors by terminating browser preflight OPTIONS requests directly at the edge.
Allowed origins are a configured list of website domains permitted to call an API from a browser. The server or gateway checks the Origin header of each request and only returns CORS permission headers, or accepts the request, when the origin is on the allowlist.
Content Security Policy (CSP) is an HTTP response header that tells browsers which sources of scripts, styles, images, and network connections a page is allowed to use. By blocking unapproved sources, CSP reduces the impact of cross-site scripting and data exfiltration.
A Reverse Proxy is an intermediate server that intercepts requests from client applications and forwards them to one or more backend origin servers. The reverse proxy terminates TLS, applies security filtering, caches responses, and returns the result to the client as if it originated from the proxy itself.
Ready-to-Use Edge Recipes
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