收到无效的Sec-WebSocket-Accept响应

Question

我正在尝试使用一段非常典型的代码连接到lichess Web套接字服务器：

    let request = NSMutableURLRequest(url: URL(string: "wss://socket.lichess.org/")!)

    self.webSocket = SRWebSocket(urlRequest: request as URLRequest!)
    self.webSocket!.delegate = self
    self.webSocket!.open()

但由于未知原因，我收到了Invalid Sec-WebSocket-Accept response：

    2017-02-28 16:01:06.724415 Lichess[58458:3046032] Optional(<CFHTTPMessageRef 0x100f08140(0x100f08150)> { parsed response, url = (null), status = 200 })
    2017-02-28 16:01:06.724563 Lichess[58458:3046032] Did fail with error: Invalid Sec-WebSocket-Accept response

我试图弄清楚过去几个小时出了什么问题，但仍无法解决问题。谁熟悉这个Sec-WebSocket-Accept，哪里可能隐藏错误？