SignalR Unable to Authentication with Certificate

Question

I would like to authenticate my signalr clients using certificate.

On the client side I have:

Connection = new HubConnection(ServerUri);
var certificate = new X509Certificate2(path);
Connection.AddClientCertificate(certificate);
HubProxy = Connection.CreateHubProxy("MyHub");

I also tried to create a certificate with private key:

var certificate = new X509Certificate2(path, "...");

On the server I have this config:

<location path="signalr">
  <system.webServer>
    <security>
      <access sslFlags="SslNegotiateCert" />
    </security>
  </system.webServer>
</location>

And to get the certificate I tried:

Context.Request.GetHttpContext().Request.ClientCertificate
Context.Request.Environment.TryGetValue("ssl.ClientCertificate", out cert)

The first problem is path="signalr". When I use this, the client cannot connect to the server and I get:

HTTP Error 500.19 - Internal Server Error
The requested page cannot be accessed because the related configuration data 
for the page is invalid.

I tried: path="~" , path="signalr/content" , path="signalr/send" and there is no error but the client certificate on the server is always null.

Any help would be greatly appreciated.