How to get value of custom http header?

Question

A custom created HTTP header whose value I need to fetch and for this, I am using following WordPress function

$response = wp_remote_get('http://example.com/page/');
$auth = wp_remote_retrieve_header( $response, 'Cache-Control' ); //Calling http header value of name "cach-control"

In above code, I am fetching a value of "Cache-Control" which is a default HTTP header. I know WordPress supports only limited HTTP header. I found one plugin that allow us to use more HTTP headers. But even with this plugin, I can't fetch the value of the custom created header.

Is there any way in which I can get the value of custom header?

Answer 1

I checked amazon.com website for retrive X-Amz-Cf-Id header which I belive is not a standard header and for me it is working fine:

function wpse_288865_featch_header() {

    $response = wp_remote_get('https://www.amazon.com/');
    $custom_header = wp_remote_retrieve_header($response, 'X-Amz-Cf-Id');

    var_dump($custom_header);
    exit;
}

add_action('init', 'wpse_288865_featch_header');

Sometimes amazon.com is not returning this header so please refresh your WordPress site couple of times.

I also inspected WordPress core for parsing request and didn't found some kind of whitelist of headers. It is only removing transfer-encoding and connection headers.

Please check if you make proper request to your site. For the first time I have checked google.com and have similar issue. I couldn't get the headers which I've seen that google.com should return. Problem was that google.com do not allow me to make such a request and in return I get HTTP/1.1 403 Forbidden response which obviously return completely different headers that HTTP/1.1 200 response.