what json structure does simple oauth expect? Drupal 8. 
I'm new with simple Oauth. 
I had manage to do this: 


But I want to do it with the Raw format, cuz my frontend is in Angular, so I will send a Json to Drupal. 

This is my first try:

{
    "grant_type":"password", 
    "client_id":"f011cc58-40ce-43a9-8f71-842494e3a997", 
    "client_secret":"abc123", 
    "username":"test", 
    "password":"test"
}


And this is the response: 


  {
      "error": "invalid_grant",
      "message": "The provided authorization grant (e.g., authorization code, resource owner credentials) or refresh token is invalid,
  expired, revoked, does not match the redirection URI used in the
  authorization request, or was issued to another client.",
      "hint": "Check the configuration to see if the grant is enabled." }


I have set up the Content-type: Application/json but I got the same result. 

Any idea??
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. 

More concrete here


  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.