Securing the API

To protect your controllers (usual one or ActionController::API) with OAuth, you just need to setup before_actions specifying the actions you want to protect. For example:

class Api::V1::ProductsController < Api::V1::ApiController
  before_action :doorkeeper_authorize! # Requires access token for all actions
  
  # before_action -> { doorkeeper_authorize! :read, :write }

  # your actions
end

You can pass any option before_action accepts, such as if, only, except, and others.

Authenticated resource owner

If you want to return data based on the current resource owner, in other words, the access token owner, you may want to define a method in your controller that returns the resource owner instance:

class Api::V1::CredentialsController < Api::V1::ApiController
  before_action :doorkeeper_authorize!
  respond_to    :json

  # GET /me.json
  def me
    respond_with current_resource_owner
  end

  private

  # Find the user that owns the access token
  def current_resource_owner
    User.find(doorkeeper_token.resource_owner_id) if doorkeeper_token
  end
end

In this example, we're returning the credentials (me.json) of the access token owner.