Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace SampleSignalRServer
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddCors(CorsOptions=>{
               CorsOptions.AddPolicy("SignalRClient",policy => {
                   policy
                   .AllowAnyHeader()
                   .AllowAnyMethod()
                   .AllowAnyOrigin();
               });
            });
            services.AddSignalR();
            services.AddMvc();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            app.UseCors("SignalRClient");
            app.UseSignalR(routes =>
            {
                routes.MapHub<Chat>("/chat");
            });
            app.UseMvc();
        }
    }
}