$options  = array (
    'http' =>
        array (
            'ignore_errors' => true,
            'method' => 'DELETE',
            'header' =>
                array (
                    0 => 'Authorization: login password',
                ),
        ),
);

$context  = stream_context_create( $options );
$response = file_get_contents(
    'https://site.com/wp-json/wp/v2/users/100?reassign=1',
    false,
    $context
);
$response = json_decode( $response );
var_dump($response);