s3+cloudfront Cross-domain problem

The cross-domain issue you're experiencing with CloudFront, despite having proper S3 CORS configuration, could be due to a few reasons:

1. Caching: CloudFront might be caching responses without the proper CORS headers. Ensure that CloudFront is set to forward the Origin header to S3, allowing S3 to send the appropriate CORS headers back.

2. Header Forwarding: Verify that your CloudFront distribution is configured to forward all necessary headers to the origin, including the 'Origin' header. This is crucial for CORS to work correctly.

3. CloudFront Behavior Settings: Double-check that your CloudFront behavior settings are correctly configured. The settings you mentioned (GET, HEAD, OPTIONS for HTTP methods, CORS-S3Origin for origin request policy, and SimpleCORS for response headers policy) seem appropriate, but ensure they are applied to the correct behavior.

4. Propagation Delays: Changes to CloudFront settings can take some time to propagate. If you've recently made changes, wait a bit and try again.

5. Cache Invalidation: If you've made changes to your CORS settings or CloudFront configuration, you may need to invalidate the CloudFront cache to ensure the new settings take effect.

6. S3 Website Endpoint: If you're using S3 static website hosting, note that CloudFront doesn't work with S3 website endpoints when using Origin Access Control (OAC). In this case, you'd need to use S3 as a regular origin, not as a website endpoint.

To troubleshoot:

1. Verify all CloudFront and S3 settings are correct.
2. Try invalidating the CloudFront cache after making changes.
3. Use browser developer tools to inspect the actual headers being returned in the response.
4. If possible, test accessing the S3 bucket directly to confirm CORS is working at the origin level.

If the issue persists after checking these points, you may need to review your CloudFront and S3 configurations more thoroughly or consider contacting AWS support for further assistance.

Sources
Static JS files served from S3 via CloudFront lead to intermittent CORS issues | AWS re:Post
Cloudfront cannot access s3 bucket | AWS re:Post
COEP and COOP response headers with S3+ Cloudfront | AWS re:Post