Merge pull request #44047 from ryanhertz/cookie-rotator

changed example cookie rotator to be in after_initialize block

guides/source/upgrading_ruby_on_rails.md

@@ -377,17 +377,20 @@ to register a rotator.
 The following is an example for rotator for the encrypted cookies.
 
 ```ruby
-Rails.application.config.action_dispatch.cookies_rotations.tap do |cookies|
-  salt = Rails.application.config.action_dispatch.authenticated_encrypted_cookie_salt
-  secret_key_base = Rails.application.secrets.secret_key_base
-
-  key_generator = ActiveSupport::KeyGenerator.new(
-    secret_key_base, iterations: 1000, hash_digest_class: OpenSSL::Digest::SHA1
-  )
-  key_len = ActiveSupport::MessageEncryptor.key_len
-  secret = key_generator.generate_key(salt, key_len)
-
-  cookies.rotate :encrypted, secret
+# config/initializers/cookie_rotator.rb
+Rails.application.config.after_initialize do
+  Rails.application.config.action_dispatch.cookies_rotations.tap do |cookies|
+    salt = Rails.application.config.action_dispatch.authenticated_encrypted_cookie_salt
+    secret_key_base = Rails.application.secrets.secret_key_base
+
+    key_generator = ActiveSupport::KeyGenerator.new(
+      secret_key_base, iterations: 1000, hash_digest_class: OpenSSL::Digest::SHA1
+    )
+    key_len = ActiveSupport::MessageEncryptor.key_len
+    secret = key_generator.generate_key(salt, key_len)
+
+    cookies.rotate :encrypted, secret
+  end
 end
 ```