POSTing in OAuth with client credentials with Doorkeeper - ruby-on-rails

Question

I've implemented a REST API and protected it with doorkeeper.
I've written a small client program to access it and it works fine using the resource owner credential flow.
Now I'm trying to implement a call using the client credentials flow. So I've followed the example in the link.
Everything works great when I'm using a GET request, but when I'm using a POST request, I'm getting a 401 Unauthorized. This is a call to a method that doesn't require a resource owner.
The only relevant thing I have in my API controller is:
doorkeeper_for :all
I haven't implemented any scopes or nothing of that kind (am I required to?).
My client code looks like this (exactly as in the example in github):
require 'rest-client'
require 'json'
client_id = 'my_client_id...'
client_secret = 'my_client_secret...'
response = RestClient.post 'http://localhost:3000/oauth/token', {
grant_type: 'client_credentials',
client_id: client_id,
client_secret: client_secret
}
token = JSON.parse(response)["access_token"]
# this line works great:
RestClient.get 'http://localhost:3000/api/v1/flights.json', { 'Authorization' => "Bearer #{token}" }
# this line always fails (401 Unauthorized):
RestClient.post 'http://localhost:3000/api/v1/flights.json', { 'Authorization' => "Bearer #{token}" }
Any idea what I may be doing wrong? Is there something special I should do in my application in order to enable the client credentials flow?

Answer 1

I figured it out. The problem was that I didn't use RestClient.post properly. The second parameter should be the payload and the third should be the header. It should be something like this:
RestClient.post 'http://localhost:3000/api/v1/flights.json', {}, { 'Authorization' => "Bearer #{token}" }