Function client_async_with_config 

pub async fn client_async_with_config<'a, R, S>(
    request: R,
    stream: S,
    config: Option<WebSocketConfig>,
) -> Result<(WebSocketStream<S>, Response<Option<Vec<u8>>>), Error>
where
    R: IntoClientRequest + Unpin,
    S: AsyncRead + AsyncWrite + Unpin,

The same as client_async() but the one can specify a websocket configuration. Please refer to client_async() for more details.