Dont confirm user on HEAD request

app/controllers/confirmations_controller.rb

@@ -1,4 +1,10 @@
 class ConfirmationsController < Devise::ConfirmationsController
+  # GET /resource/confirmation?confirmation_token=abcdef
+  # HEAD request on confirmation URL must not confirm the user
+  def show
+    request.head? ? head(:ok) : super
+  end
+
   private
 
   def after_confirmation_path_for(_resource_name, resource)

spec/controllers/confirmations_controller_spec.rb

@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe ConfirmationsController, type: :controller do
+  include Rails.application.routes.url_helpers
+
+  describe '#show' do
+    let(:user) { create(:user, confirmed_at: nil) }
+    let(:token) { user.confirmation_token }
+
+    before do
+      request.env['devise.mapping'] = Devise.mappings[:user]
+      user.send_confirmation_instructions
+    end
+
+    context 'with HEAD' do
+      before do
+        head :show, params: { confirmation_token: token }
+      end
+
+      it 'does not redirect' do
+        expect(response).to be_successful
+      end
+
+      it 'does not confirm the user' do
+        expect(user.reload.confirmed?).to be(false)
+      end
+    end
+
+    context 'with GET' do
+      before do
+        get :show, params: { confirmation_token: token }
+      end
+
+      it 'redirects' do
+        uri = URI.parse(response.location)
+        params = Rack::Utils.parse_nested_query(uri.query)
+
+        expect(uri.path).to eq('/users/password/edit')
+        expect(params).to include('confirmed' => 'true')
+        expect(params).to include('reset_password_token' => a_string_matching(/\A.+\z/))
+      end
+
+      it 'confirms the user' do
+        expect(user.reload.confirmed?).to be(true)
+      end
+    end
+  end
+end