Initialize the Micropub extension if it was not given app
        in the constructor.

        Args:
          app (flask.Flask): the flask application to extend.
          client_id (string, optional): the IndieAuth client id, will be
            displayed when the user is asked to authorize this client. If not
            provided, the app name will be used.

def init_app(self, app, client_id=None):
        """Initialize the Micropub extension if it was not given app
        in the constructor.

        Args:
          app (flask.Flask): the flask application to extend.
          client_id (string, optional): the IndieAuth client id, will be
            displayed when the user is asked to authorize this client. If not
            provided, the app name will be used.
        """
        if not self.client_id:
            if client_id:
                self.client_id = client_id
            else:
                self.client_id = app.name