Add invisible_captcha on the user registration page

The default action when a user submit the form too quickly is to
redirect to :back with flash error message. As we are using CableReady
it's not working for us, so I render_alert_timestamp_error_message
to show the error message to the user.

app/controllers/spree/users_controller.rb

@@ -8,6 +8,7 @@ module Spree
 
     layout 'darkswarm'
 
+    invisible_captcha only: [:create], on_timestamp_spam: :render_alert_timestamp_error_message
     skip_before_action :set_current_order, only: :show
     prepend_before_action :load_object, only: [:show, :edit, :update]
     prepend_before_action :authorize_actions, only: :new
@@ -101,5 +102,16 @@ module Spree
     def user_params
       ::PermittedAttributes::User.new(params).call
     end
+
+    def render_alert_timestamp_error_message
+      render cable_ready: cable_car.inner_html(
+        "#signup-feedback",
+        partial("layouts/alert",
+                locals: {
+                  type: "alert",
+                  message: InvisibleCaptcha.timestamp_error_message
+                })
+      )
+    end
   end
 end

app/views/layouts/_signup_tab.html.haml

@@ -23,3 +23,4 @@
     .row
       .large-12.columns
         = form.submit t(:action_signup), { class: "button primary", tabindex: 4 }
+        = form.invisible_captcha 

config/initializers/invisible_captcha.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+InvisibleCaptcha.setup do |config|
+  # Disable timestamp check for test environment
+  config.timestamp_enabled = !Rails.env.test?
+end

spec/system/consumer/authentication_spec.rb

@@ -108,6 +108,21 @@ describe "Authentication" do
             expect(page).to have_content "doesn't match"
           end
 
+          it "Failing to sign up because the user is too quick" do
+            InvisibleCaptcha.timestamp_enabled = true
+            InvisibleCaptcha.timestamp_threshold = 30
+
+            fill_in "Your email", with: user.email
+            fill_in "Choose a password", with: "test12345"
+            fill_in "Confirm password", with: "test12345"
+            click_signup_button
+
+            expect(page).to have_content "Sorry, that was too quick! Please resubmit."
+
+            InvisibleCaptcha.timestamp_enabled = false
+            InvisibleCaptcha.timestamp_threshold = 30
+          end
+
           it "Signing up successfully" do
             fill_in "Your email", with: "test@foo.com"
             fill_in "Choose a password", with: "test12345"