Expose Use as a public method on WAB (#38011)

- Added a test to verify that it is publicly callable

Author: davidfowl

src/DefaultBuilder/src/PublicAPI.Unshipped.txt

@@ -25,6 +25,7 @@ Microsoft.AspNetCore.Builder.WebApplication.Services.get -> System.IServiceProvi
 Microsoft.AspNetCore.Builder.WebApplication.StartAsync(System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.Task!
 Microsoft.AspNetCore.Builder.WebApplication.StopAsync(System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.Task!
 Microsoft.AspNetCore.Builder.WebApplication.Urls.get -> System.Collections.Generic.ICollection<string!>!
+Microsoft.AspNetCore.Builder.WebApplication.Use(System.Func<Microsoft.AspNetCore.Http.RequestDelegate!, Microsoft.AspNetCore.Http.RequestDelegate!>! middleware) -> Microsoft.AspNetCore.Builder.IApplicationBuilder!
 Microsoft.AspNetCore.Builder.WebApplicationBuilder
 Microsoft.AspNetCore.Builder.WebApplicationBuilder.Build() -> Microsoft.AspNetCore.Builder.WebApplication!
 Microsoft.AspNetCore.Builder.WebApplicationBuilder.Configuration.get -> Microsoft.Extensions.Configuration.ConfigurationManager!

src/DefaultBuilder/src/WebApplication.cs

@@ -181,7 +181,12 @@ IApplicationBuilder IApplicationBuilder.New()
             return newBuilder;
         }
 
-        IApplicationBuilder IApplicationBuilder.Use(Func<RequestDelegate, RequestDelegate> middleware)
+        /// <summary>
+        /// Adds the middleware to the application request pipeline.
+        /// </summary>
+        /// <param name="middleware">The middleware.</param>
+        /// <returns>An instance of <see cref="IApplicationBuilder"/> after the operation has completed.</returns>
+        public IApplicationBuilder Use(Func<RequestDelegate, RequestDelegate> middleware)
         {
             ApplicationBuilder.Use(middleware);
             return this;

src/DefaultBuilder/test/Microsoft.AspNetCore.Tests/WebApplicationTests.cs

@@ -1835,6 +1835,26 @@ public void ConfigurationProviderTypesArePreserved()
             Assert.Single(((IConfigurationRoot)app.Configuration).Providers.OfType<RandomConfigurationProvider>());
         }
 
+        [Fact]
+        public async Task CanUseMiddleware()
+        {
+            var builder = WebApplication.CreateBuilder();
+            builder.WebHost.UseTestServer();
+            await using var app = builder.Build();
+
+            app.Use(next =>
+            {
+                return context => context.Response.WriteAsync("Hello World");
+            });
+
+            await app.StartAsync();
+
+            var client = app.GetTestClient();
+
+            var response = await client.GetStringAsync("/");
+            Assert.Equal("Hello World", response);
+        }
+
         public class RandomConfigurationSource : IConfigurationSource
         {
             public int ProvidersBuilt { get; set; }