<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def init_app(self, app):
 # type: (Flask) -> None """Register the extension on the given Flask application. Use this function only when no Flask application was provided in the ``app`` keyword argument to the constructor of this class. The function sets ``True`` defaults for :py:const:`VERIFY_SIGNATURE_APP_CONFIG` and :py:const:`VERIFY_TIMESTAMP_APP_CONFIG` configurations. It adds the skill id: self instance mapping to the application extensions, and creates a :py:class:`ask_sdk_webservice_support.webservice_handler.WebserviceHandler` instance, for request verification and dispatch. :param app: A :py:class:`flask.Flask` application instance :type app: flask.Flask :rtype: None """

        app.config.setdefault(VERIFY_SIGNATURE_APP_CONFIG, True)
        app.config.setdefault(VERIFY_TIMESTAMP_APP_CONFIG, True)

        if EXTENSION_NAME not in app.extensions:
            app.extensions[EXTENSION_NAME] = {}

        app.extensions[EXTENSION_NAME][self._skill_id] = self

        with app.app_context():
            self._create_webservice_handler(self._skill, self._verifiers)