- during validation stage:
            Event 1: validate_resource
                - run on each Module in URL path
                - binders:
                    - cb_users_*
                        - load user_id into context
                    - cb_accounts
                        - load account_db/accout_id into context

            Event 2: validate
                - only run on last Module, like resource_exists

        If only resource_exists() method took Context as parameter, could fold o