It will depend if the backend can receive a JSON format. 

In my case, I am working with the Drupal 8 Module simple Oauth. and the The format for OAuth 2.0 Bearer tokens is actually described in a separate spec, [RFC 6750][1]. 

More concrete [here][2]

> The entity-body follows the encoding requirements of the
> "application/x-www-form-urlencoded" content-type as defined by HTML
> 4.01 [W3C.REC-html401-19991224].

So, In my particular case, I will try to send a form-data from angular. 



  [1]: https://tools.ietf.org/html/rfc6750
  [2]: https://tools.ietf.org/html/rfc6750#page-4