How to use authogic without requiring a password

user.rb

class User < ActiveRecord::Base
  acts_as_authentic do |config|
    config.validate_password_field :if => :require_password_on_signup?
  end
  
  def require_password_on_signup?
    false
  end
end

user_test.rb

require 'test_helper'

class UserTest < ActiveSupport::TestCase
  test "password requirement" do
    @user = User.new
    @user.valid?
    assert_equal [], @user.errors[:password]
  end
end