JsonapiForRails

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base # or ActionController::API

  # Enable JSONAPI
  acts_as_jsonapi_resources(
    # links:               false,
    # content_negotiation: false
  )

  # ...
end

# app/controllers/articles_controller.rb

# Change the API controller's parent class
class ArticlesController < JsonapiResourcesController
  # ...
end

# Do the same with AuthorsController

# config/routes.rb
Rails.application.routes.draw do
  # ...

  scope '/api/v1' do # Optional scoping

    [ # List your API controllers here
      :articles, :authors
    ].each do |resources_name|
      resources resources_name do
        controller resources_name do
          get     'relationships/:relationship', action: "relationship_show"
          patch   'relationships/:relationship', action: "relationship_update"
          post    'relationships/:relationship', action: "relationship_add"
          delete  'relationships/:relationship', action: "relationship_remove"
        end
      end
    end

  end

  # ...
end

# app/controllers/jsonapi_resources_controller.rb
class JsonapiResourcesController < ApplicationController
  acts_as_jsonapi_resources

  before_action :authenticate

private
  def authenticate
    # ...
  end
end

# app/controllers/jsonapi_resources_controller.rb
class JsonapiResourcesController < ApplicationController
  acts_as_jsonapi_resources

  before_action :permit_read, only: [
    :index,
    :show,
    :relationship_show
  ]

  before_action :permit_write, only: [
    :create, 
    :update, 
    :destroy,
    :relationship_update,
    :relationship_add,
    :relationship_remove
  ]

private
  def permit_read
    # ...
  end

  def permit_write
    # ...
  end
end

# app/controllers/articles_controller.rb
class ArticlesController < JsonapiResourcesController 

  def index
    # These model-related utility methods are available inside all action methods.
    jsonapi_model_class # =>  Article
    jsonapi_model_type  # => :articles

    # @jsonapi_links indicates whether links should be included in response documents.
    # It is available inside all action methods.
    @jsonapi_links      # => true

    # ...
  end

  def show
    # @jsonapi_record contains the current database record.
    # It is available inside all action methods (including all relationship
    # methods) except :index and :create.
    @jsonapi_record.to_jsonapi_hash        # => {data:   {...}}
    @jsonapi_record.to_jsonapi_errors_hash # => {errors: [...]}

    # ...
  end

  def relationship_show
    # @jsonapi_relationship is available in all relationship action methods.
    # @jsonapi_relationship[:definition] describes the current relationship.
    @jsonapi_relationship # => {:definition=>{:name=>:author, :type=>:to_one, :receiver=>{:type=>:authors, :class=>Author}}}

    # ...
  end

  def relationship_update
    # @jsonapi_relationship[:params] contains the parsed request body.
    # It is available for all relationship action methods except relationship_show.
    # @jsonapi_relationship[:params][:data] behaves like a Hash for relationships
    # of type :to_one, and as an Array for relationships of type :to_many.
    @jsonapi_relationship # => {:definition=>{...}, :params=>{"data"=>{"type"=>"authors", "id"=>"234455384"}}}

    # ...
  end

end