Inherit config from ActionController::Base

By using an inheritable_copy of the config (rather than just redefining
the methods) we gain the ability to _override_ the config locally.

Author: nevans

lib/omniauth/rails_csrf_protection/token_verifier.rb

@@ -13,19 +13,20 @@ module RailsCsrfProtection
     # authenticity token, you can find the source code at
     # https://github.com/rails/rails/blob/v5.2.2/actionpack/lib/action_controller/metal/request_forgery_protection.rb#L217-L240.
     class TokenVerifier
+      # Inherits config from ActionController::Base.
+      # Define _before_ including ActionController::RequestForgeryProtection.
+      def self.config
+        @_config ||= ActionController::Base.config.inheritable_copy
+      end
+
       include ActiveSupport::Configurable
       include ActionController::RequestForgeryProtection
 
       # `ActionController::RequestForgeryProtection` contains a few
       # configurable options. As we want to make sure that our configuration is
       # the same as what being set in `ActionController::Base`, we should make
-      # all out configuration methods to delegate to `ActionController::Base`.
-      config.each_key do |configuration_name|
-        undef_method configuration_name
-        define_method configuration_name do
-          ActionController::Base.config[configuration_name]
-        end
-      end
+      # our configuration delegate to `ActionController::Base`.
+      config.each_key do |key| config.delete(key) end
 
       def call(env)
         dup._call(env)