configuration_controller.rb

class ConfigurationController < ApiController
  def index
    render jsonapi: {
      footer_text: 'CopyRight',
      footer_color: '#FFF',
      footer_logo: 's3_iamge_path',
    }
  end
end

class ConfigurationSerializer < JSONAPI::Serializable::Resource
  attributes :footer_text, :footer_color, :footer_logo
end