exporter: add IExporter and Exporter impl

Add new 'export' component that can export a certificate to a file on
disk from a certificate provider.

src/Sign.Core/Exporter.cs

@@ -0,0 +1,72 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE.txt file in the project root for more information.
+
+using System.Diagnostics;
+using System.Security.Cryptography.X509Certificates;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+
+namespace Sign.Core;
+
+internal class Exporter : IExporter
+{
+    private readonly IServiceProvider _serviceProvider;
+    private readonly ILogger<IExporter> _logger;
+
+    // Dependency injection requires a public constructor.
+    public Exporter(IServiceProvider serviceProvider, ILogger<IExporter> logger)
+    {
+        ArgumentNullException.ThrowIfNull(serviceProvider, nameof(serviceProvider));
+        ArgumentNullException.ThrowIfNull(logger, nameof(logger));
+
+        _serviceProvider = serviceProvider;
+        _logger = logger;
+    }
+
+    public async Task<int> ExportAsync(string outputPath)
+    {
+        try
+        {
+            ICertificateProvider certificateProvider = _serviceProvider.GetRequiredService<ICertificateProvider>();
+            using (X509Certificate2 certificate = await certificateProvider.GetCertificateAsync())
+            {
+                _logger.LogInformation(Resources.FetchedCertificateFingerprint, certificate.Thumbprint);
+
+                // Write out copy of public part of certificate if an output path was given
+                if (!string.IsNullOrWhiteSpace(outputPath))
+                {
+                    // Ensure parent directory exists
+                    string? parentDir = Path.GetDirectoryName(outputPath);
+                    if (parentDir is not null && !Directory.Exists(parentDir))
+                    {
+                        _logger.LogDebug(Resources.CreatingDirectory, parentDir);
+                        Directory.CreateDirectory(parentDir);
+                    }
+
+                    // Clean up any existing file
+                    if (File.Exists(outputPath))
+                    {
+                        _logger.LogDebug(Resources.DeletingFile, outputPath);
+                        File.Delete(outputPath);
+                        _logger.LogDebug(Resources.DeletedFile, outputPath);
+                    }
+
+                    _logger.LogInformation(Resources.ExportingCertificate, outputPath);
+
+                    var sw = Stopwatch.StartNew();
+                    byte[] data = certificate.Export(X509ContentType.Cert);
+                    await File.WriteAllBytesAsync(outputPath, data);
+                    _logger.LogInformation(Resources.ExportSucceededWithTimeElapsed, sw.ElapsedMilliseconds);
+                }
+            }
+        }
+        catch (Exception e)
+        {
+            _logger.LogError(e, e.Message);
+            return ExitCode.Failed;
+        }
+
+        return ExitCode.Success;
+    }
+}

src/Sign.Core/IExporter.cs

@@ -0,0 +1,10 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE.txt file in the project root for more information.
+
+namespace Sign.Core;
+
+internal interface IExporter
+{
+    Task<int> ExportAsync(string outputPath);
+}

src/Sign.Core/Resources.resx

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <root>
   <!-- 
     Microsoft ResX Schema 
@@ -168,6 +168,14 @@
     <value>Deleting directory {path}.</value>
     <comment>{Placeholder="{path}"} is a directory path.</comment>
   </data>
+  <data name="DeletedFile" xml:space="preserve">
+    <value>File {path} deleted.</value>
+    <comment>{Placeholder="{path}"} is a file path.</comment>
+  </data>
+  <data name="DeletingFile" xml:space="preserve">
+    <value>Deleting file {path}.</value>
+    <comment>{Placeholder="{path}"} is a file path.</comment>
+  </data>
   <data name="DirectoryNotDeleted" xml:space="preserve">
     <value>Directory {path} still exists.</value>
     <comment>{Placeholder="{path}"} is a directory path.</comment>
@@ -183,10 +191,22 @@
     <value>An exception occurred while attempting to delete directory {path}.</value>
     <comment>{Placeholder="{path}"} is a directory path.</comment>
   </data>
+  <data name="ExportingCertificate" xml:space="preserve">
+    <value>Exporting certificate to {path}.</value>
+    <comment>{Placeholder="{path}"} is a path to a certificate file.</comment>
+  </data>
+  <data name="ExportSucceededWithTimeElapsed" xml:space="preserve">
+    <value>Completed in {millseconds} ms.</value>
+    <comment>{Placeholder="{milliseconds}"} is a decimal number representing the number of milliseconds elapsed, and "ms" is the unit abbreviation for milliseconds.</comment>
+  </data>
   <data name="FetchedCertificate" xml:space="preserve">
     <value>Fetched certificate. [{milliseconds} ms]</value>
     <comment>{Placeholder="{milliseconds}"} is a decimal number representing the number of milliseconds elapsed, and "ms" is the unit abbreviation for milliseconds.</comment>
   </data>
+  <data name="FetchedCertificateFingerprint" xml:space="preserve">
+    <value>Fetched certificate with fingerprint {fingerprint}.</value>
+    <comment>{Placeholder="{fingerprint}"} is an identifier for a certificate.</comment>
+  </data>
   <data name="FetchingCertificate" xml:space="preserve">
     <value>Fetching certificate from Azure Key Vault.</value>
   </data>

src/Sign.Core/ServiceProvider.cs

@@ -76,6 +76,7 @@ internal static ServiceProvider CreateDefault(
             services.AddSingleton<IVsixSignTool, VsixSignTool>();
             services.AddSingleton<ICertificateVerifier, CertificateVerifier>();
             services.AddSingleton<ISigner, Signer>();
+            services.AddSingleton<IExporter, Exporter>();
 
             if (addServices is not null)
             {
@@ -85,4 +86,4 @@ internal static ServiceProvider CreateDefault(
             return new ServiceProvider(services.BuildServiceProvider());
         }
     }
-}
+}