Add Solidus admin unauthorized redirect handler

If someone just requests '/admin' without being logged in Solidus
renders '/unauthorized'. In solidus_auth_devise there is a redirect
handler for this case that redirects to '/login'. In case we do not
have solidus_auth_devise we need to provide a handler that redirects
to Alchemy.login_path.

Refs AlchemyCMS#32

lib/alchemy/solidus/engine.rb

@@ -26,6 +26,7 @@ class Engine < ::Rails::Engine
         if Alchemy.user_class_name == 'Alchemy::User'
           require 'alchemy/solidus/alchemy_user_extension'
           Alchemy::User.include Alchemy::Solidus::AlchemyUserExtension
+          require 'alchemy/solidus/spree_admin_unauthorized_redirect'
         end
 
         if SolidusSupport.solidus_gem_version < Gem::Version.new('2.5')

lib/alchemy/solidus/spree_admin_unauthorized_redirect.rb

@@ -0,0 +1,9 @@
+Spree::Admin::BaseController.unauthorized_redirect = -> do
+  if try_spree_current_user
+    flash[:error] = I18n.t('spree.authorization_failure')
+    redirect_to spree.root_path
+  else
+    store_location
+    redirect_to alchemy.login_path
+  end
+end

lib/generators/alchemy/solidus/install/install_generator.rb

@@ -45,7 +45,7 @@ def run_spree_custom_user_generator
         if Kernel.const_defined?('Alchemy::Devise') && !options[:skip_spree_custom_user_generator]
           arguments = options[:auto_accept] ? ['Alchemy::User', '--force'] : ['Alchemy::User']
           Spree::CustomUserGenerator.start(arguments)
-          gsub_file 'lib/spree/authentication_helpers.rb', /main_app\./, 'alchemy.'
+          gsub_file 'lib/spree/authentication_helpers.rb', /main_app\./, 'Alchemy.'
           if SolidusSupport.solidus_gem_version < Gem::Version.new('2.5.0')
             gsub_file 'config/initializers/spree.rb', /Spree\.user_class.?=.?.+$/, 'Spree.user_class = "Alchemy::User"'
           end

spec/features/alchemy/alchemy_admin_integrations_spec.rb

@@ -7,6 +7,12 @@
 require 'spree/testing_support/factories/address_factory'
 
 RSpec.feature "Admin Integration", type: :feature do
+  it 'gets redirected to login if accessing admin' do
+    visit '/admin'
+
+    expect(page).to have_field 'user_login'
+  end
+
   it 'it is possible to login and visit Alchemy admin' do
     login!
     visit '/admin/dashboard'