api.array :users do
  @users.each do |user|
    api.user do
      api.id         user.id
      api.login      user.login
      api.firstname  user.firstname
      api.lastname   user.lastname
      api.mail       user.mail
      api.created_on user.created_on
      api.last_login_on user.last_login_on

      api.array :custom_fields do
        user.visible_custom_field_values.each do |custom_value|
          api.custom_field custom_value.value, :id => custom_value.custom_field_id, :name => custom_value.custom_field.name
        end
      end unless user.visible_custom_field_values.empty?
    end
  end
end