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add_action( 'init', 'handle_preflight' );

function handle_preflight() {
    header("Access-Control-Allow-Origin: " . get_http_origin());
    header("Access-Control-Allow-Methods: POST, GET, OPTIONS, PUT, DELETE");
    header("Access-Control-Allow-Credentials: true");

    if ( 'OPTIONS' == $_SERVER['REQUEST_METHOD'] ) {
        status_header(200);
        exit();
    }
}