Updated CHANGELOG, docs, guides and release notes.

Also added a `cookies_serializer.rb` initializer to the app template.

1 files changed, 13 insertions, 0 deletions

diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index 2055452935..8aae3bbc1a 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -98,6 +98,19 @@ If your test helper contains a call to
 is now done automatically when you `require 'test_help'`, although
 leaving this line in your helper is not harmful in any way.
 
+### Cookies serializer
+
+Applications created before Rails 4.1 uses `Marshal` to serialize cookie values into
+the signed and encrypted cookie jars. If you want to use the new `JSON`-based format
+in your application, you can add an initializer file with the following content:
+
+  ```ruby
+  Rails.application.config.cookies_serializer :hybrid
+  ```
+
+This would transparently migrate your existing `Marshal`-serialized cookies into the
+new `JSON`-based format.
+
 ### Changes in JSON handling
 
 There are a few major changes related to JSON handling in Rails 4.1.