def __call__(
        self, environ: WSGIEnvironment, start_response: StartResponse
    ) -> cabc.Iterable[bytes]:
        """The WSGI server calls the Flask application object as the
        WSGI application. This calls :meth:`wsgi_app`, which can be
        wrapped to apply middleware.
        """
        return self.wsgi_app(environ, start_response)
The WSGI server calls the Flask application object as the
        WSGI application. This calls :meth:`wsgi_app`, which can be
        wrapped to apply middleware.
        
src/flask/app.py