Error thrown when calling HubConnection.Start: StatusCode: 401, ReasonPhrase: 'Incoming principal is null'

Question

I am using SignalR with my WebApi application and that works fine: the client connects to the hub using WebSocket transport and the user is authenticated with some custom middleware authentication.

I am trying to connect to this hub from another backend application (.NET client) and to do this I make a hub connection and create a hub proxy, then invoke the hub method:

string auth = "someEncryptedValue"
HubConnection hubConn = new HubConnection("myUrl");
hubConn.Headers.Add("myauthtoken", auth);
IHubProxy proxy = hubConn.CreateHubProxy("hubName");
Task t = Task.Run(() => hubConn.Start(new LongPollingTransport()));
t.WaitAndUnwrap // An extension method
hubProxy.Invoke("SendMessage", message);

The exception is thrown when t.WaitAndUnwrap() is called (the extension method is not the issue). I had this incoming principal is null issue before I added the http header token (which, of course, is not actually the literal string "someEncryptedValue"). So I added that here and then I added a custom authorization class for the hub back in my other application:

public class HeadersAuthAttribute : AuthorizeAttribute
{
    public override bool AuthroizeHubConnection(HubDescriptor hubDescriptor, IRequest request)
    {
        string auth = request.Headers["myauthtoken"];
        if (auth == "someEncryptedValue") //again, this is actually more complex than shown here
        {
            return true;
        }
        else
        {
            // Need to check if the incoming principal is authenticated in case
            // the connection to the hub is being made the normal way through the
            // WebApi instead of the proxy using http headers
            return request.User?.Identity?.IsAuthenticated ?? false;
        }
        return false;
    }
}

And of course my hub has the headers attribute:

[HeadersAuth]
public class MyHub : Hub
{
    // Hub logic
}

However, after running this I still get the incoming principal is null error. Then I read that you cannot use custom http headers with WebSockets, which is why I put new LongPollingTransport() in the hubConn.Start call above. But that didn't seem to change anything, at least not the error I get.

Does anyone know what can be going on? It'd be nice if I could debug the code with the actual hub and authorization so I can see what's going on when the hubConn.Start call is made. Is there a way I can check the http header is set correctly and fetched correctly? If the error is about the incoming principal being null, is authentication even the issue? Could it be another part of the code where it's trying to find the user? I'm not sure what to do about that since this hub connection is being made from a .NET client. Also, I know the HeadersAuthAttribute class is being called and is used correctly when connecting to the hub normally using WebSockets since it goes into the else case where it checks that the IIdentity is authenticated.

Just to add a bit more of what I've tried:

I made the auth string token purposefully wrong to see if I get a different error, but I still get incoming principal is null.
I realized that my OnConnected() override method for my hub calls a method that tries to use the incoming principal with this.Context.User without checking if it's null. I removed that and anything else that tries to use the incoming principal in the hub, but unfortunately it still gives the same error.

score 0 · Accepted Answer · edited May 23 '17 at 12:33

I figured out what was wrong. It wasn't to do with the hub authentication, as I suspected as I was finishing this post. What was happening was my Startup file makes the call app.ConfigureAuth, but this eventually leads to some custom authorization in the OWIN middleware pipeline that checks if the incoming principal is null. I've taken that out for SignalR connections.

It should also be noted that after I got that working I couldn't make hub method calls from the proxy because it wasn't authorized to do so. To fix that I added

public override bool AuthorizeHubMethodInvocation(IHubIncomingInvokerContext hubIncomingInvokerContext, bool appliesToMethod)

to the HeadersAuthAttribute class, which I got from here.

Error thrown when calling HubConnection.Start: StatusCode: 401, ReasonPhrase: 'Incoming principal is null'

1 Answers1