Add new Microsoft.AspNetCore.SpaServices.Extensions package to host new runtime functionality needed for updated templates until 2.1 ships

src/Microsoft.AspNetCore.SpaServices.Extensions/SpaApplicationBuilderExtensions.cs

@@ -0,0 +1,46 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.SpaServices;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
+using System;
+
+namespace Microsoft.AspNetCore.Builder
+{
+    /// <summary>
+    /// Provides extension methods used for configuring an application to
+    /// host a client-side Single Page Application (SPA).
+    /// </summary>
+    public static class SpaApplicationBuilderExtensions
+    {
+        /// <summary>
+        /// Handles all requests from this point in the middleware chain by returning
+        /// the default page for the Single Page Application (SPA).
+        /// 
+        /// This middleware should be placed late in the chain, so that other middleware
+        /// for serving static files, MVC actions, etc., takes precedence.
+        /// </summary>
+        /// <param name="app">The <see cref="IApplicationBuilder"/>.</param>
+        /// <param name="configuration">
+        /// This callback will be invoked so that additional middleware can be registered within
+        /// the context of this SPA.
+        /// </param>
+        public static void UseSpa(this IApplicationBuilder app, Action<ISpaBuilder> configuration)
+        {
+            if (configuration == null)
+            {
+                throw new ArgumentNullException(nameof(configuration));
+            }
+
+            // Use the options configured in DI (or blank if none was configured). We have to clone it
+            // otherwise if you have multiple UseSpa calls, their configurations would interfere with one another.
+            var optionsProvider = app.ApplicationServices.GetService<IOptions<SpaOptions>>();
+            var options = new SpaOptions(optionsProvider.Value);
+
+            var spaBuilder = new DefaultSpaBuilder(app, options);
+            configuration.Invoke(spaBuilder);
+            SpaDefaultPageMiddleware.Attach(spaBuilder);
+        }
+    }
+}