wp_get_current_user() function not working under custom endpoint.

I cannot get wp_get_current_user() on my custom WordPress endpoint.

function spinwrite_endpoint() {
  register_rest_route('spinwrite', '/rewriter/', Array(
    'methods' => 'GET',
    'callback' => Array($this, 'rewriter')
  ));
}

function rewriter( $request ) {
  return wp_get_current_user();
}

When I go to mywebsite.com/wp-json/spinwrite/rewriter when I am logged in, it gives me a response as though I’m not logged in.

{"data":{},"ID":0,"caps":[],"cap_key":null,"roles":[],"allcaps":[],"filter":null}

Also, I’ve tried other functions that access the user such as . . .
is_user_in_role('edit_posts');
. . . and WordPress treats me as though I’m logged out and have no permissions.

This is really important to get working because I can’t secure my endpoint without some form of checking who is accessing it.

I did try installing the WP REST API v2 plugin, but then my endpoint disappeared and when I uninstalled the WP REST API v2 plugin my endpoint was still gone. I had to completely reinstall WordPress just to get it to work again.

I don’t want to use an external plugin for my endpoint authentication if I can help it anyways because then my plugin is dependant on it.