Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using provider.Repositories;
// using provider.Middleware; // STEP_9

namespace Provider
{
    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.AddSingleton<IProductRepository, ProductRepository>();
            services.AddControllers()
                        .AddJsonOptions(options => options.JsonSerializerOptions.WriteIndented = true);
            services.AddMvc();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            // app.UseMiddleware<AuthorizationMiddleware>(); // STEP_9
            app.UseRouting();
            app.UseEndpoints(e => e.MapControllers());
            
        }
    }
}