Cross-Origin-Opener-Policy
The HTTP Cross-Origin-Opener-Policy (COOP) response header allows you to ensure a top-level document does not share a browsing context group with cross-origin documents.
COOP will process-isolate your document and potential attackers can't access to your global object if they were opening it in a popup, preventing a set of cross-origin attacks dubbed XS-Leaks.
If a cross-origin document with COOP is opened in a new window, the opening document will not have a reference to it, and the window.opener property of the new window will be null. This allows you to have more control over references to a window than rel=noopener, which only affects outgoing navigations.
Certain features like SharedArrayBuffer objects or Performance.now() with unthrottled timers are only available if your document has a COOP header with the value same-origin value set.
