Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.FileProviders;
using System.IO;

namespace DAB.Api
{
	public class Startup
	{
		public Startup(IConfiguration configuration, IHostingEnvironment environment)
		{
			Configuration = configuration;
			Environment = environment;
		}

		public IConfiguration Configuration { get; }
		public IHostingEnvironment Environment { get; }

		// This method gets called by the runtime. Use this method to add services to the container.
		public void ConfigureServices(IServiceCollection services)
		{
			...
		}

		// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
		public void Configure(IApplicationBuilder app)
		{
			...
			bool isWwwRequest(HttpContext context) => context.Request.Host.Host.ToLower().Contains("www");

			var rootPath = Environment.IsDevelopment()
				? "../AngularApps"
				: "AngularApps";

			var aboutPath = Path.Combine(Environment.ContentRootPath, $"{rootPath}/about");
			var webPath = Path.Combine(Environment.ContentRootPath, $"{rootPath}/web");

			app.UseWhen(context => isWwwRequest(context), appBuilder =>
			{
				appBuilder.UseStaticFiles(new StaticFileOptions()
				{
					FileProvider = new PhysicalFileProvider(aboutPath),
				});

				appBuilder.Run(async context =>
				{
					await context.Response.SendFileAsync(Path.Combine(aboutPath, "index.html"));
					return;
				});
			});

			app.UseStaticFiles(new StaticFileOptions()
			{
				FileProvider = new PhysicalFileProvider(webPath),
			});

			app.Run(async context =>
			{
				await context.Response.SendFileAsync(Path.Combine(webPath, "index.html"));
				return;
			});
		}
	}
}