public HttpHeaders generatePreflightResponseHeaders() {
        final HttpHeadersBuilder headers = HttpHeaders.builder();
        preflightResponseHeaders.forEach((key, value) -> {
            final Object val = getValue(value);
            if (val instanceof Iterable) {
                headers.addObject(key, (Iterable<?>) val);
            } else {
                headers.addObject(key, val);
            }
        });
        return headers.build();
    }
Generates immutable HTTP response headers that should be added to a CORS preflight response.

@return {@link HttpHeaders} the HTTP response headers to be added.
core/src/main/java/com/linecorp/armeria/server/cors/CorsPolicy.java