discourse/app/controllers/steps_controller.rb

require_dependency 'wizard'
require_dependency 'wizard/builder'
require_dependency 'wizard/step_updater'

class StepsController < ApplicationController

  before_action :ensure_wizard_enabled
  before_action :ensure_logged_in
  before_action :ensure_admin

  def update
    wizard = Wizard::Builder.new(current_user).build
    updater = wizard.create_updater(params[:id], params[:fields])
    updater.update

    if updater.success?
      result = { success: 'OK' }
      result[:refresh_required] = true if updater.refresh_required?
      render json: result
    else
      errors = []
      updater.errors.messages.each do |field, msg|
        errors << { field: field, description: msg.join }
      end
      render json: { errors: errors }, status: 422
    end
  end

end