I am hosting a website using 1and1 (ionos), and it is serving a HTML page with imported CSS and JS. I am trying to figure out how to enable cross origin isolation, but all I can find is that we need to enable certain response headers: https://web.dev/cross-origin-isolation-guide/.
Specifically in these instructions:
What does it mean to set a header on a top-level document? How does one accomplish this? I have done plenty of searching but have not found details on how to create/enable these response headers.
I need to do this in order to use SharedArrayBuffer in Firefox.