Register IApplicationDiscriminator service

src/Microsoft.AspNetCore.Hosting/Internal/ApplicationDiscriminator.cs

@@ -0,0 +1,25 @@
+// 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.DataProtection.Infrastructure;
+
+namespace Microsoft.AspNetCore.Hosting.Internal
+{
+    public class ApplicationDiscriminator : IApplicationDiscriminator
+    {
+        private readonly IHostingEnvironment _hostingEnvironment;
+
+        public ApplicationDiscriminator(IHostingEnvironment hostingEnvironment)
+        {
+            if (hostingEnvironment == null)
+            {
+                throw new ArgumentNullException(nameof(hostingEnvironment));
+            }
+
+            _hostingEnvironment = hostingEnvironment;
+        }
+
+        public string Discriminator => _hostingEnvironment.ContentRootPath;
+    }
+}

src/Microsoft.AspNetCore.Hosting/Microsoft.AspNetCore.Hosting.csproj

@@ -17,6 +17,7 @@
   </ItemGroup>
 
   <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.DataProtection.Abstractions" Version="$(AspNetCoreVersion)" />
     <PackageReference Include="Microsoft.AspNetCore.Http" Version="$(AspNetCoreVersion)" />
     <PackageReference Include="Microsoft.AspNetCore.Http.Extensions" Version="$(AspNetCoreVersion)" />
     <PackageReference Include="Microsoft.Extensions.Configuration" Version="$(AspNetCoreVersion)" />

src/Microsoft.AspNetCore.Hosting/WebHostBuilder.cs

@@ -7,6 +7,7 @@ using System.Diagnostics;
 using System.IO;
 using System.Reflection;
 using System.Runtime.ExceptionServices;
+using Microsoft.AspNetCore.DataProtection.Infrastructure;
 using Microsoft.AspNetCore.Hosting.Builder;
 using Microsoft.AspNetCore.Hosting.Internal;
 using Microsoft.AspNetCore.Http;
@@ -303,6 +304,7 @@ namespace Microsoft.AspNetCore.Hosting
             var services = new ServiceCollection();
             services.AddSingleton(_hostingEnvironment);
             services.AddSingleton(_context);
+            services.AddTransient<IApplicationDiscriminator, ApplicationDiscriminator>();
 
             var builder = new ConfigurationBuilder()
                 .SetBasePath(_hostingEnvironment.ContentRootPath)

test/Microsoft.AspNetCore.Hosting.Tests/WebHostBuilderTests.cs

@@ -9,6 +9,7 @@ using System.Reflection;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.DataProtection.Infrastructure;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Hosting.Fakes;
 using Microsoft.AspNetCore.Hosting.Internal;
@@ -987,6 +988,19 @@ namespace Microsoft.AspNetCore.Hosting
             Assert.IsType<FileNotFoundException>(ex.InnerExceptions[0].InnerException);
         }
 
+        [Fact]
+        public void Build_SetsAppDescriminatorFromContentRoot()
+        {
+            var builder = CreateWebHostBuilder()
+                .UseContentRoot(Environment.CurrentDirectory)
+                .Configure(app => { })
+                .UseServer(new TestServer());
+
+            var host = builder.Build();
+            var applicationDiscriminator = host.Services.GetRequiredService<IApplicationDiscriminator>();
+            Assert.Equal(Environment.CurrentDirectory, applicationDiscriminator.Discriminator);
+        }
+
         [Fact]
         public async Task Build_DoesNotThrowIfUnloadableAssemblyNameInHostingStartupAssembliesAndCaptureStartupErrorsTrue()
         {