Startup.cs

using HttpTracer;
using System.Net.Http;
using Microsoft.AspNetCore.Components.Browser;
using Microsoft.AspNetCore.Components.Builder;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.AspNetCore.Components;
using System;
using Microsoft.AspNetCore.Blazor.Services;
using Microsoft.AspNetCore.Blazor.Http;

namespace WebApplication1
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddSingleton<HttpClient>(s =>
            {
                // Creating the URI helper needs to wait until the JS Runtime is initialized, so defer it.
                var uriHelper = s.GetRequiredService<IUriHelper>();
                return new HttpClient(new HttpTracerHandler(new WebAssemblyHttpMessageHandler()))
                {
                    BaseAddress = new Uri(WebAssemblyUriHelper.Instance.GetBaseUri())
                };
            });
        }

        public void Configure(IComponentsApplicationBuilder app)
        {
            app.AddComponent<App>("app");
        }
    }
}