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 6750RFC 6750.
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.