Rails 8.2 drops Marshal message fallback

Rails 8.2 changes config.active_support.message_serializer to :json for applications using config.load_defaults 8.2 . This change is merged on Rails main; Rails 8.2 is not yet released. The 7.1 through 8.1 defaults already write JSON, but accept older Marshal messages through :json_allow_marshal . The new default stops accepting Marshal when reading messages through ActiveSupport::MessageVerifier and ActiveSupport::MessageEncryptor . That can affect older Marshal-serialized tokens read throug...