Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using VueCliMiddleware;

namespace AspNetCoreVueStarter
{
    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.AddControllersWithViews();

            // Add AddRazorPages if the app uses Razor Pages.
            // services.AddRazorPages();

            // In production, the Vue files will be served from this directory
            services.AddSpaStaticFiles(configuration =>
            {
                configuration.RootPath = "ClientApp/dist";
            });
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {

            _ = CommandLine.Arguments.TryGetOptions(System.Environment.GetCommandLineArgs(), false, out string mode, out ushort port, out bool https);

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            if (https) app.UseHttpsRedirection();

            app.UseStaticFiles();
            if (!env.IsDevelopment())
            {
                app.UseSpaStaticFiles();
            }

            app.UseRouting();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller}/{action=Index}/{id?}");

                // Add MapRazorPages if the app uses Razor Pages. Since Endpoint Routing includes support for many frameworks, adding Razor Pages is now opt -in.
                // endpoints.MapRazorPages();
            });

            app.UseSpa(spa =>
            {
                // To learn more about options for serving an Angular SPA from ASP.NET Core,
                // see https://go.microsoft.com/fwlink/?linkid=864501

                spa.Options.SourcePath = "ClientApp";

                if (env.IsDevelopment())
                {

                    // run npm process with client app
                    if (mode == "start") {
                        spa.UseVueCli(npmScript: "serve", port: port, forceKill: true, https: https);
                    }

                    // if you just prefer to proxy requests from client app, use proxy to SPA dev server instead,
                    // app should be already running before starting a .NET client:
                    // run npm process with client app
                    if (mode == "attach") {
                        spa.UseProxyToSpaDevelopmentServer($"{(https ? "https" : "http")}://localhost:{port}"); // your Vue app port
                    }
                }
            });
        }
    }
}