Websocket server unable to negotiate Sec-Websocket-Protocol

[bramley-jetcharge]

My client sends a supported sub protocol in Sec-Websocket-Protocol. I only want to accept the connection if the client sends ocpp1.6.
I implemented it like this:

class DeviceWsSession : WsSession{

    public override bool OnWsConnecting(HttpRequest request, HttpResponse response)
    {
        string subProtocol=null;
        for (int i = 0; i < deviceRequestContext.Headers; i++)
        {
            var header = deviceRequestContext.Header(i);
            if(header.Item1.Equals("Sec-WebSocket-Protocol", StringComparison.OrdinalIgnoreCase)){
                subProtocol = header.Item2;
                break;
            }
        }
        if(subProtocol!="ocpp1.6"){
        //unsupported subprotocol, reject the connection
            response.MakeErrorResponse((int)HttpStatusCode.BadRequest, "unsupported subprotocol");
            Close();
            return false;
        }
        response.SetHeader("Sec-WebSocket-Protocol", subProtocol);
        return true;
        
    }
}

issue 1:

The client is not receiving the selected subprotocol header, and closes the connection. This is easy to reproduce in eg Postman:

Error: Server sent no subprotocol

Handshake Details
Request Method: GET
Status Code: 101 Switching Protocols
Request Headers
Sec-WebSocket-Version: 13
Sec-WebSocket-Key: Hr7wRgkSPHil966y7gpxVw==
Connection: Upgrade
Upgrade: websocket
Sec-WebSocket-Protocol: ocpp1.6
Sec-WebSocket-Extensions: permessage-deflate; client_max_window_bits
Host: localhost:1102

Response Headers
Connection: Upgrade
Upgrade: websocket
Sec-WebSocket-Accept: AInRhNxNz2oZImm00u32GUcaRn0=
Content-Length: 0

If I remove all of my code, simply return true in OnWsConnecting instead, the same behaviour occurs (seemingly because the library does not send a subprotocol out-of-the-box, fair enough).

issue 2:

In the case where the client sends an unexpected subprotocol I can't support, I want to gracefully close the connection instead. With the above code, Postman shows this error:
Error: Parse Error: Expected HTTP/
Instead of showing the Http 400 bad request, so this is not a graceful disconnect.

I am able to achieve the expected results in Postman using other websocket server libraries, so I'm not sure if this is a limitation of this library or if I'm doing it in the wrong sequence.

Cheers