In the ASP.NET version it's extremely simple:
hubConnection.Credentials = CredentialCache.DefaultNetworkCredentials;
How can I accomplish this in the new AspNetCore C# managed client?
You can do this within the options of "WithUrl"
HubConnection connection = new HubConnectionBuilder()
.WithUrl("/chatHub", o => { o.Credentials = CredentialCache.DefaultNetworkCredentials; })
.Build();