I think you are the one who doesn't know what they are on about.
First, the header must be added to the response, not the request.
Second, in many environments (managed hosting etc.) there is not an easy way (or indeed a way at all) of adding headers to responses.
What are you talking about. Any non-static hosting will let you specify headers with a plain php function. Any baseline shared hosting offers that kind of control and has done so for the past 20+ years.
is that something that could have be done in the dot file for server override? what was it, .htaccess or something?
> Second, in many environments (managed hosting etc.) there is not an easy way (or indeed a way at all) of adding headers to responses.
It's getting better. Most serverless hosts (including Cloudflare, which this site uses) follow the (req: Request) => Response pattern, which by definition allows sending headers.