Normalize data protection app discriminator (#41095)

Author: HaoK

src/DataProtection/DataProtection/src/Internal/HostingApplicationDiscriminator.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.IO;
 using Microsoft.AspNetCore.DataProtection.Infrastructure;
 using Microsoft.Extensions.Hosting;
 
@@ -20,5 +21,6 @@ public HostingApplicationDiscriminator(IHostEnvironment hosting)
         _hosting = hosting;
     }
 
-    public string? Discriminator => _hosting?.ContentRootPath;
+    // Note: ContentRootPath behavior depends on the version, sometimes it has a trailing slash, we normalize by default by removing a trailing slash
+    public string? Discriminator => _hosting?.ContentRootPath?.TrimEnd(Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar);
 }

src/DataProtection/DataProtection/test/HostingTests.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.DataProtection.Infrastructure;
 using Microsoft.AspNetCore.DataProtection.KeyManagement.Internal;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Hosting.Server;
@@ -16,6 +17,28 @@ namespace Microsoft.AspNetCore.DataProtection.Test;
 
 public class HostingTests
 {
+    [Fact]
+    public void DefaultApplicationDiscriminatorTrimsTrailingSlash()
+    {
+        var builder = new WebHostBuilder()
+            .UseStartup<TestStartup>()
+            .ConfigureServices(s => s.AddDataProtection());
+
+        using (var host = builder.Build())
+        {
+            var contentRootPath = host.Services.GetRequiredService<IWebHostEnvironment>().ContentRootPath;
+            Assert.True(contentRootPath.EndsWith(Path.DirectorySeparatorChar), "expected contentRootPath to end with a slash");
+
+            var appDisc = host.Services.GetRequiredService<IApplicationDiscriminator>().Discriminator;
+            Assert.False(appDisc.EndsWith(Path.DirectorySeparatorChar), "expected appDiscriminator to have slash trimmed");
+            Assert.False(appDisc.EndsWith(Path.AltDirectorySeparatorChar), "expected appDiscriminator to have slash trimmed");
+
+            var appId = host.Services.GetApplicationUniqueIdentifier();
+            Assert.False(appId.EndsWith(Path.DirectorySeparatorChar), "expected appId to have slash trimmed");
+            Assert.False(appId.EndsWith(Path.AltDirectorySeparatorChar), "expected appId to have slash trimmed");
+        }
+    }
+
     [Fact]
     public async Task WebhostLoadsKeyRingBeforeServerStarts()
     {