feat: add omniauthable config

Author: zernie

README.md

@@ -52,6 +52,19 @@ Devise.setup do |config|
 end
 ```
 
+### Omniauthable
+
+To enable Devise's Omniauthable module, you must follow the [devise wiki](https://github.com/heartcombo/devise/wiki/OmniAuth:-Overview) with _just one exception_:
+Instead of adding 
+```ruby
+devise :omniauthable, omniauth_providers: %i[...]
+```
+you should add this line to an initializer (typically `config/initializers/spree.rb`):
+
+```ruby
+Spree::Auth::Config[:omniauthable_providers] = %i[...]
+```
+
 Using in an existing application
 --------------------------------
 

app/models/spree/user.rb

@@ -9,6 +9,7 @@ class User < Spree::Base
     devise :database_authenticatable, :registerable, :recoverable,
            :rememberable, :trackable, :validatable, :encryptable
     devise :confirmable if Spree::Auth::Config[:confirmable]
+    devise :omniauthable, omniauth_providers: Spree::Auth::Config[:omniauthable] if Spree::Auth::Config[:omniauthable].present?
 
     acts_as_paranoid
     after_destroy :scramble_email_and_password

lib/spree/auth_configuration.rb

@@ -5,6 +5,7 @@ class AuthConfiguration < Preferences::Configuration
     preference :registration_step, :boolean, default: true
     preference :signout_after_password_change, :boolean, default: true
     preference :confirmable, :boolean, default: false
+    preference :omniauthable_providers, :array, default: []
     preference :draw_frontend_routes, :boolean, default: true
     preference :draw_backend_routes, :boolean, default: true
   end

spec/models/user_spec.rb

@@ -96,4 +96,14 @@
       expect(Spree::User.ancestors).not_to include(Devise::Models::Confirmable)
     end
   end
+
+  describe "omniauthable" do
+    it "loads Devise's :omniauthable module when :omniauthable is set", omniauthable: %[twitter] do
+      expect(Spree::User.ancestors).to include(Devise::Models::Omniauthable)
+    end
+
+    it "does not load Devise's :omniauthable module when :omniauthable is nil", omniauthable: nil do
+      expect(Spree::User.ancestors).not_to include(Devise::Models::Omniauthable)
+    end
+  end
 end

spec/support/omniauthable_helpers.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+RSpec.configure do |config|
+  config.before do |example|
+    if example.metadata.key?(:omniauthable)
+      stub_spree_preferences(Spree::Auth::Config, omniauthable: example.metadata[:omniauthable])
+
+      # load File.expand_path('../../../app/models/spree/user.rb', __FILE__)
+    end
+  end
+end