Use authenticated cookie options to disable embedding of the expiration in the cookies

We were generating the cookie value with the expiry information embedded what
makes the value impossible to be read by a Rails 5.1 application.

This option is only useful if you need to share your cookies between
a Rails 5.1 and a Rails 5.2 application, or if you are still validating
the deploy and wants to eventually rollback.

actionpack/lib/action_dispatch/middleware/cookies.rb

@@ -490,10 +490,14 @@ def request; @parent_jar.request; end
 
       private
         def expiry_options(options)
-          if options[:expires].respond_to?(:from_now)
-            { expires_in: options[:expires] }
+          if request.use_authenticated_cookie_encryption
+            if options[:expires].respond_to?(:from_now)
+              { expires_in: options[:expires] }
+            else
+              { expires_at: options[:expires] }
+            end
           else
-            { expires_at: options[:expires] }
+            {}
           end
         end
 

actionpack/test/dispatch/cookies_test.rb

@@ -1283,6 +1283,18 @@ def test_signed_cookie_with_expires_set_relatively
     assert_nil cookies.signed[:user_name]
   end
 
+  def test_signed_cookie_does_not_embed_expiration_if_config_is_set_to_false
+    @request.env['action_dispatch.use_authenticated_cookie_encryption'] = false
+
+    cookies.signed[:user_name] = { value: "assain", expires: 2.hours }
+
+    travel 1.hour
+    assert_equal "assain", cookies.signed[:user_name]
+
+    travel 2.hours
+    assert_equal "assain", cookies.signed[:user_name]
+  end
+
   def test_encrypted_cookie_with_expires_set_relatively
     cookies.encrypted[:user_name] = { value: "assain", expires: 2.hours }
 
@@ -1293,6 +1305,18 @@ def test_encrypted_cookie_with_expires_set_relatively
     assert_nil cookies.encrypted[:user_name]
   end
 
+  def test_encrypted_cookie_does_not_embed_expiration_if_config_is_set_to_false
+    @request.env['action_dispatch.use_authenticated_cookie_encryption'] = false
+
+    cookies.encrypted[:user_name] = { value: "assain", expires: 2.hours }
+
+    travel 1.hour
+    assert_equal "assain", cookies.encrypted[:user_name]
+
+    travel 2.hours
+    assert_equal "assain", cookies.encrypted[:user_name]
+  end
+
   def test_vanilla_cookie_with_expires_set_relatively
     travel_to Time.utc(2017, 8, 15) do
       get :cookie_expires_in_two_hours

guides/source/configuring.md

@@ -502,6 +502,10 @@ Defaults to `'signed cookie'`.
 * `config.action_dispatch.cookies_rotations` allows rotating
   secrets, ciphers, and digests for encrypted and signed cookies.
 
+* `config.action_dispatch.use_authenticated_cookie_encryption` controls encrypted cookies to use AES-256-GC
+  authenticated encryption and if signed and encrypted cookies are going to embed the expiry information
+  in the value. It defaults to `false`.
+
 * `config.action_dispatch.perform_deep_munge` configures whether `deep_munge`
   method should be performed on the parameters. See [Security Guide](security.html#unsafe-query-generation)
   for more information. It defaults to `true`.

guides/source/upgrading_ruby_on_rails.md

@@ -76,6 +76,17 @@ Rails 5.2 adds bootsnap gem in the [newly generated app's Gemfile](https://githu
 The `app:update` task sets it up in `boot.rb`. If you want to use it, then add it in the Gemfile,
 otherwise change the `boot.rb` to not use bootsnap.
 
+### Expiry in signed or encrypted cookie is now embedded in the cookies values
+
+To improve security, Rails now embeds the expiry information also in encrypted or signed cookies value.
+
+This new embed information make those cookies incompatible with versions of Rails older than 5.2.
+
+If you require your cookies to be read by 5.1 and older, or you are still validating your 5.2 deploy and want
+to allow you to rollback set
+`Rails.application.config.action_dispatch.use_authenticated_cookie_encryption` to `false`.
+
+
 Upgrading from Rails 5.0 to Rails 5.1
 -------------------------------------
 

railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults_5_2.rb.tt

@@ -11,6 +11,11 @@
 # Rails.application.config.active_record.cache_versioning = true
 
 # Use AES-256-GCM authenticated encryption for encrypted cookies.
+# Also, embed cookie expiry in signed or encrypted cookies for increased security.
+#
+# This option is not backwards compatible with earlier Rails versions.
+# It's best enabled when your entire app is migrated and stable on 5.2.
+#
 # Existing cookies will be converted on read then written with the new scheme.
 # Rails.application.config.action_dispatch.use_authenticated_cookie_encryption = true