Add ActionController::Base.skip_forgery_protection

Since we now default to `protect_from_forgery with: :exception`,
provide a wrapper to `skip_before_action :verify_authenticity_token`
for disabling forgery protection.

actionpack/lib/action_controller/metal/request_forgery_protection.rb

@@ -132,6 +132,15 @@ module ActionController #:nodoc:
         append_after_action :verify_same_origin_request
       end
 
+      # Turn off request forgery protection. This is a wrapper for:
+      #
+      #   skip_before_action :verify_authenticity_token
+      #
+      # See +skip_before_action+ for allowed options.
+      def skip_forgery_protection(options = {})
+        skip_before_action :verify_authenticity_token, options
+      end
+
       private
 
         def protection_method_class(name)

actionpack/test/controller/request_forgery_protection_test.rb

@@ -163,6 +163,13 @@ class PerFormTokensController < ActionController::Base
   end
 end
 
+class SkipProtectionController < ActionController::Base
+  include RequestForgeryProtectionActions
+  protect_from_forgery with: :exception
+  skip_forgery_protection if: :skip_requested
+  attr_accessor :skip_requested
+end
+
 # common test methods
 module RequestForgeryProtectionTests
   def setup
@@ -964,3 +971,26 @@ class PerFormTokensControllerTest < ActionController::TestCase
       assert_equal expected, actual
     end
 end
+
+class SkipProtectionControllerTest < ActionController::TestCase
+  def test_should_not_allow_post_without_token_when_not_skipping
+    @controller.skip_requested = false
+    assert_blocked { post :index }
+  end
+
+  def test_should_allow_post_without_token_when_skipping
+    @controller.skip_requested = true
+    assert_not_blocked { post :index }
+  end
+
+  def assert_blocked
+    assert_raises(ActionController::InvalidAuthenticityToken) do
+      yield
+    end
+  end
+
+  def assert_not_blocked
+    assert_nothing_raised { yield }
+    assert_response :success
+  end
+end