code: def init_app(self, app):
          
          # Save this so we can use it later in the extension
          if not hasattr(app, 'extensions'):   # pragma: no cover
              app.extensions = {}
          app.extensions['flask-jwt-simple'] = self
  
          # Set all the default configurations for this extension
          self._set_default_configuration_options(app)
          self._set_error_handler_callbacks(app)
  
          # Set propagate exceptions, so all of our error handlers properly
          # work in production
          app.config['PROPAGATE_EXCEPTIONS'] = True
docs: Register this extension with the flask app
  
          :param app: A flask application