Allow suppressing the use of environment variables

src/Hosting/Hosting/src/GenericHost/GenericWebHostBuilder.cs

@@ -29,13 +29,18 @@ internal class GenericWebHostBuilder : IWebHostBuilder, ISupportsStartup, ISuppo
         private AggregateException _hostingStartupErrors;
         private HostingStartupWebHostBuilder _hostingStartupWebHostBuilder;
 
-        public GenericWebHostBuilder(IHostBuilder builder)
+        public GenericWebHostBuilder(IHostBuilder builder, WebHostBuilderOptions options)
         {
             _builder = builder;
+            var configBuilder = new ConfigurationBuilder()
+                .AddInMemoryCollection();
 
-            _config = new ConfigurationBuilder()
-                .AddEnvironmentVariables(prefix: "ASPNETCORE_")
-                .Build();
+            if (!options.SuppressEnvironmentConfiguration)
+            {
+                configBuilder.AddEnvironmentVariables(prefix: "ASPNETCORE_");
+            }
+
+            _config = configBuilder.Build();
 
             _builder.ConfigureHostConfiguration(config =>
             {

src/Hosting/Hosting/src/GenericHostWebHostBuilderExtensions.cs

@@ -1,3 +1,6 @@
+// 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 System;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.DependencyInjection;
@@ -6,9 +9,37 @@ namespace Microsoft.Extensions.Hosting
 {
     public static class GenericHostWebHostBuilderExtensions
     {
+        /// <summary>
+        /// Adds and configures an ASP.NET Core web application.
+        /// </summary>
         public static IHostBuilder ConfigureWebHost(this IHostBuilder builder, Action<IWebHostBuilder> configure)
         {
-            var webhostBuilder = new GenericWebHostBuilder(builder);
+            if (configure is null)
+            {
+                throw new ArgumentNullException(nameof(configure));
+            }
+
+            return builder.ConfigureWebHost(configure, _ => { });
+        }
+
+        /// <summary>
+        /// Adds and configures an ASP.NET Core web application.
+        /// </summary>
+        public static IHostBuilder ConfigureWebHost(this IHostBuilder builder, Action<IWebHostBuilder> configure, Action<WebHostBuilderOptions> configureWebHostBuilder)
+        {
+            if (configure is null)
+            {
+                throw new ArgumentNullException(nameof(configure));
+            }
+
+            if (configureWebHostBuilder is null)
+            {
+                throw new ArgumentNullException(nameof(configureWebHostBuilder));
+            }
+
+            var webHostBuilderOptions = new WebHostBuilderOptions();
+            configureWebHostBuilder(webHostBuilderOptions);
+            var webhostBuilder = new GenericWebHostBuilder(builder, webHostBuilderOptions);
             configure(webhostBuilder);
             builder.ConfigureServices((context, services) => services.AddHostedService<GenericWebHostService>());
             return builder;

src/Hosting/Hosting/src/WebHostBuilderOptions.cs

@@ -0,0 +1,17 @@
+// 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.
+
+namespace Microsoft.Extensions.Hosting
+{
+    /// <summary>
+    /// Builder options for use with ConfigureWebHost.
+    /// </summary>
+    public class WebHostBuilderOptions
+    {
+        /// <summary>
+        /// Indicates if "ASPNETCORE_" prefixed environment variables should be added to configuration.
+        /// They are added by default.
+        /// </summary>
+        public bool SuppressEnvironmentConfiguration { get; set; } = false;
+    }
+}

src/Hosting/Hosting/test/Fakes/GenericWebHostBuilderWrapper.cs

@@ -16,7 +16,7 @@ public class GenericWebHostBuilderWrapper : IWebHostBuilder, ISupportsStartup, I
 
         internal GenericWebHostBuilderWrapper(HostBuilder hostBuilder)
         {
-            _builder = new GenericWebHostBuilder(hostBuilder);
+            _builder = new GenericWebHostBuilder(hostBuilder, new WebHostBuilderOptions());
             _hostBuilder = hostBuilder;
         }
 

src/Hosting/Hosting/test/GenericWebHostBuilderTests.cs

@@ -0,0 +1,41 @@
+// 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 System;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Hosting
+{
+    // Most functionality is covered by WebHostBuilderTests for compat. Only GenericHost specific functionality is covered here.
+    public class GenericWebHostBuilderTests
+    {
+        [Fact]
+        public void ReadsAspNetCoreEnvironmentVariables()
+        {
+            var randomEnvKey = Guid.NewGuid().ToString();
+            Environment.SetEnvironmentVariable("ASPNETCORE_" + randomEnvKey, "true");
+            using var host = new HostBuilder()
+                .ConfigureWebHost(_ => { })
+                .Build();
+            var config = host.Services.GetRequiredService<IConfiguration>();
+            Assert.Equal("true", config[randomEnvKey]);
+            Environment.SetEnvironmentVariable("ASPNETCORE_" + randomEnvKey, null);
+        }
+
+        [Fact]
+        public void CanSuppressAspNetCoreEnvironmentVariables()
+        {
+            var randomEnvKey = Guid.NewGuid().ToString();
+            Environment.SetEnvironmentVariable("ASPNETCORE_" + randomEnvKey, "true");
+            using var host = new HostBuilder()
+                .ConfigureWebHost(_ => { }, webHostBulderOptions => { webHostBulderOptions.SuppressEnvironmentConfiguration  = true; })
+                .Build();
+            var config = host.Services.GetRequiredService<IConfiguration>();
+            Assert.Null(config[randomEnvKey]);
+            Environment.SetEnvironmentVariable("ASPNETCORE_" + randomEnvKey, null);
+        }
+    }
+}

src/Hosting/Hosting/test/WebHostBuilderTests.cs

@@ -6,19 +6,15 @@
 using System.IO;
 using System.Linq;
 using System.Reflection;
-using System.Runtime.ExceptionServices;
 using System.Threading;
 using System.Threading.Tasks;
-using System.Web;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Hosting.Fakes;
 using Microsoft.AspNetCore.Hosting.Server;
 using Microsoft.AspNetCore.Hosting.Tests.Fakes;
 using Microsoft.AspNetCore.Http;
-using Microsoft.AspNetCore.Http.Extensions;
 using Microsoft.AspNetCore.Http.Features;
-using Microsoft.AspNetCore.WebUtilities;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;