ASP.NET Core SignalR chat with Angular 5 - https://codingblast.com/asp-net-core-signalr-chat-angular

Startup.cs

services.AddCors(o => o.AddPolicy("CorsPolicy", builder =>
    {
        builder
        .AllowAnyMethod()
        .AllowAnyHeader()
        .WithOrigins("http://localhost:4200");
    }));