Cross-Origin-Embedder-Policy

unsafe-none

This is the default value. Allows the document to fetch cross-origin resources without giving explicit permission through the CORS protocol or the Cross-Origin-Resource-Policy header.

require-corp

A document can only load resources from the same origin, or resources explicitly marked as loadable from another origin. If a cross origin resource supports CORS, the crossorigin attribute or the Cross-Origin-Resource-Policy header must be used to load it without being blocked by COEP.

credentialless

no-cors cross-origin requests are sent without credentials. In particular, it means Cookies are omitted from the request, and ignored from the response. The responses are allowed without an explicit permission via the Cross-Origin-Resource-Policy header. Navigate responses behave similarly as the require-corp mode: They require Cross-Origin-Resource-Policy response header.

Certain features, such as access to SharedArrayBuffer objects or using Performance.now() with unthrottled timers, are only available if your document is cross-origin isolated.

To use these features in a document, you will need to set the COEP header with a value of require-corp or credentialless, and the Cross-Origin-Opener-Policy header to same-origin. In addition the feature must not be blocked by Permissions-Policy: cross-origin-isolated.

Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: require-corp

You can use the Window.crossOriginIsolated and WorkerGlobalScope.crossOriginIsolated properties to check if the features are restricted in window and worker contexts, respectively:

const myWorker = new Worker("worker.js");

if (crossOriginIsolated) {
  const buffer = new SharedArrayBuffer(16);
  myWorker.postMessage(buffer);
} else {
  const buffer = new ArrayBuffer(16);
  myWorker.postMessage(buffer);
}

If you enable COEP using require-corp and have a cross origin resource that needs to be loaded, it needs to support CORS and you need to explicitly mark the resource as loadable from another origin to avoid blockage from COEP. For example, you can use the crossorigin attribute for this image from a third-party site:

<img src="https://thirdparty.com/img.png" crossorigin />

If CORS is not supported for some images, a COEP value of credentialless can be used as an alternative to load the image without any explicit opt-in from the cross-origin server, at the cost of requesting it without cookies.

• Cross-Origin-Opener-Policy