CODE EXAMPLE FOR PHP

header cross origin using php only for our domains and subdomain

$allowedOrigins = [
    "http://www.websiteA.com",
    "https://www.websiteB.com"
    // ... etc
];

if (in_array($_SERVER["HTTP_ORIGIN"], $allowedOrigins)) {
    header("Access-Control-Allow-Origin: " . $_SERVER["HTTP_ORIGIN"]);
}