Custom Spree Devise Registration - Admin Authorization Failure

I have added name, surname and birthdate fields to devise registration. Here is the link to my original question.

Adding name to Spree Devise registration

It seems that on the frontend side everything works. However I now get an Authorization Failure alert when I try to access my admin.

Here is the console log:

Started GET "/admin/orders" for ::1 at 2015-07-21 13:25:16 -0500
Processing by Spree::Admin::OrdersController#index as HTML
  Spree::Preference Load (0.3ms)  SELECT  "spree_preferences".* FROM "spree_preferences" WHERE "spree_preferences"."key" = $1 LIMIT 1  [["key", "spree/backend_configuration/locale"]]
  Spree::User Load (0.5ms)  SELECT  "spree_users".* FROM "spree_users" WHERE "spree_users"."deleted_at" IS NULL AND "spree_users"."id" = $1  ORDER BY "spree_users"."id" ASC LIMIT 1  [["id", 6]]
   (0.7ms)  SELECT COUNT(*) FROM "spree_roles" INNER JOIN "spree_roles_users" ON "spree_roles"."id" = "spree_roles_users"."role_id" WHERE "spree_roles_users"."user_id" = $1 AND "spree_roles"."name" = $2  [["user_id", 6], ["name", "admin"]]
Redirected to http://localhost:3000/unauthorized
Completed 302 Found in 88ms (ActiveRecord: 4.1ms)

I have tried to override app/controllers/spree/admin/users_controller_decorator.rb

module Spree
  module Admin
   UsersController.class_eval do

    private
     def user_params
         params.require(:user).permit(:email, :password, :password_confirmation, :spree_role_ids, :name, :surname, :birthdate)

     end

   end
  end
end

You Cant asign a role admin to any user from frontend side. Please register a user from front end and change it role from backend.