Add ability to set hCaptcha either on registration form or on e-mail validation

Upshot of CAPTCHA on e-mail validation is it does not need to break the in-band
registration API.

app/controllers/auth/confirmations_controller.rb

@@ -1,12 +1,18 @@
 # frozen_string_literal: true
 
 class Auth::ConfirmationsController < Devise::ConfirmationsController
+  include CaptchaConcern
+
   layout 'auth'
 
   before_action :set_body_classes
   before_action :set_pack
+  before_action :set_confirmation_user!, only: [:show, :confirm_captcha]
   before_action :require_unconfirmed!
 
+  before_action :extend_csp_for_captcha!, only: [:show, :confirm_captcha]
+  before_action :require_captcha_if_needed!, only: [:show]
+
   skip_before_action :require_functional!
 
   def new
@@ -15,8 +21,52 @@ class Auth::ConfirmationsController < Devise::ConfirmationsController
     resource.email = current_user.unconfirmed_email || current_user.email if user_signed_in?
   end
 
+  def show
+    clear_captcha!
+
+    old_session_values = session.to_hash
+    reset_session
+    session.update old_session_values.except('session_id')
+
+    super
+  end
+
+  def confirm_captcha
+    check_captcha! do |message|
+      flash.now[:alert] = message
+      render :captcha
+      return
+    end
+
+    show
+  end
+
   private
 
+  def require_captcha_if_needed!
+    render :captcha if captcha_required?
+  end
+
+  def set_confirmation_user!
+    # We need to reimplement looking up the user because
+    # Devise::ConfirmationsController#show looks up and confirms in one
+    # step.
+    confirmation_token = params[:confirmation_token]
+    return if confirmation_token.nil?
+    @confirmation_user = User.find_first_by_auth_conditions(confirmation_token: confirmation_token)
+  end
+
+  def captcha_user_bypass?
+    return true if @confirmation_user.nil? || @confirmation_user.confirmed?
+
+    invite = Invite.find(@confirmation_user.invite_id) if @confirmation_user.invite_id.present?
+    invite.present? && !invite.max_uses.nil?
+  end
+
+  def captcha_context
+    'email-confirmation'
+  end
+
   def set_pack
     use_pack 'auth'
   end