Problems with Unity WebGL Cross-Origin Resource Sharing, Safari and S3

Hello!

We have some clients that use proxy servers so in order to get our Unity WebGL apps working properly we modified the UnityLoader.js and app_name.js files to add withCredentials = true to all of our XMLHttpRequests.

This works well in all browers except Safari. For some reason, in Safari adding withCredentials = true causes Access-Control-Allow-Origin errors (Origin is not allowed by Access-Control-Allow-Origin. Failed to load resource). This is true in Safari whether we use the proxy server or not when withCredentials = true. If we remove withCredentials = true, it works outside of the proxy.

Has anyone experienced this before? Our WebGL files are on S3 (behind a CDN). I'm not sure why Safari is behaving differently than the other browsers.

Thanks,
Jared