Feature/get debug view value processing

src/libraries/Common/tests/Extensions/ConfigurationRootTest.cs

@@ -11,6 +11,8 @@ namespace Microsoft.Extensions.Configuration.Test
 {
     public class ConfigurationRootTest
     {
+        private const string SecretCover = "*****";
+
         [Fact]
         public void RootDisposesProviders()
         {
@@ -76,12 +78,56 @@ public void ChainedConfigurationIsDisposed(bool shouldDispose)
             Assert.Equal(shouldDispose, provider.IsDisposed);
         }
 
+        [Fact]
+        public void SecretsAreConcealed()
+        {
+            var provider = new SecretConfigurationProvider("secret", "secret-value");
+
+            var config = new ConfigurationRoot(new IConfigurationProvider[] {
+                provider
+            });
+
+            var debugView = config.GetDebugView(ProcessValue);
+
+            Assert.Contains(SecretCover, debugView);
+        }
+
+        [Fact]
+        public void NonSecretsAreNotConcealed()
+        {
+            var provider = new TestConfigurationProvider("foo", "foo-value");
+
+            var config = new ConfigurationRoot(new IConfigurationProvider[] {
+                provider
+            });
+
+            var debugView = config.GetDebugView(ProcessValue);
+
+            Assert.DoesNotContain(SecretCover, debugView);
+        }
+
+        private string ProcessValue(ConfigurationDebugViewContext context)
+        {
+            if (context.ConfigurationProvider.ToString() == nameof(SecretConfigurationProvider))
+            {
+                return SecretCover;
+            }
+
+            return context.Value;
+        }
+
         private class TestConfigurationProvider : ConfigurationProvider
         {
             public TestConfigurationProvider(string key, string value)
                 => Data.Add(key, value);
         }
 
+        private class SecretConfigurationProvider : ConfigurationProvider
+        {
+            public SecretConfigurationProvider(string key, string value)
+                => Data.Add(key, value);
+        }
+
         private class DisposableTestConfigurationProvider : ConfigurationProvider, IDisposable
         {
             public bool IsDisposed { get; set; }

src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs

@@ -32,6 +32,15 @@ public static partial class ConfigurationPath
     public static partial class ConfigurationRootExtensions
     {
         public static string GetDebugView(this Microsoft.Extensions.Configuration.IConfigurationRoot root) { throw null; }
+        public static string GetDebugView(this IConfigurationRoot root, System.Func<ConfigurationDebugViewContext, string>? processValue) { throw null; }
+    }
+    public readonly partial struct ConfigurationDebugViewContext
+    {
+        public ConfigurationDebugViewContext(string path, string key, string? value, IConfigurationProvider configurationProvider) { throw null; }
+        public string Path { get; }
+        public string Key { get; }
+        public string? Value { get; }
+        public IConfigurationProvider ConfigurationProvider { get; }
     }
     public partial interface IConfiguration
     {

src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationDebugViewContext.cs

@@ -0,0 +1,39 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.Extensions.Configuration
+{
+    /// <summary>
+    /// Provides the data about current item of the configuration.
+    /// </summary>
+    public readonly struct ConfigurationDebugViewContext
+    {
+        public ConfigurationDebugViewContext(string path, string key, string? value, IConfigurationProvider configurationProvider)
+        {
+            Path = path;
+            Key = key;
+            Value = value;
+            ConfigurationProvider = configurationProvider;
+        }
+
+        /// <summary>
+        /// Gets the path of the current item.
+        /// </summary>
+        public string Path { get; }
+
+        /// <summary>
+        /// Gets the key of the current item.
+        /// </summary>
+        public string Key { get; }
+
+        /// <summary>
+        /// Gets the value of the current item.
+        /// </summary>
+        public string? Value { get; }
+
+        /// <summary>
+        /// Gets the <see cref="IConfigurationProvider" /> that was used to get the value of the current item.
+        /// </summary>
+        public IConfigurationProvider ConfigurationProvider { get; }
+    }
+}

src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationRootExtensions.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;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
@@ -17,6 +18,22 @@ public static class ConfigurationRootExtensions
         /// </summary>
         /// <returns> The debug view. </returns>
         public static string GetDebugView(this IConfigurationRoot root)
+        {
+            return GetDebugView(root, processValue: null);
+        }
+
+        /// <summary>
+        /// Generates a human-readable view of the configuration showing where each value came from.
+        /// </summary>
+        /// <param name="root">Configuration root</param>
+        /// <param name="processValue">
+        /// Function for processing the value e.g. hiding secrets
+        /// Parameters:
+        ///   ConfigurationDebugViewContext: Context of the current configuration item
+        ///   returns: A string value is used to assign as the Value of the configuration section
+        /// </param>
+        /// <returns> The debug view. </returns>
+        public static string GetDebugView(this IConfigurationRoot root, Func<ConfigurationDebugViewContext, string>? processValue)
         {
             void RecurseChildren(
                 StringBuilder stringBuilder,
@@ -29,11 +46,15 @@ void RecurseChildren(
 
                     if (valueAndProvider.Provider != null)
                     {
+                        string? value = processValue != null
+                            ? processValue(new ConfigurationDebugViewContext(child.Key, child.Path, valueAndProvider.Value, valueAndProvider.Provider))
+                            : valueAndProvider.Value;
+
                         stringBuilder
                             .Append(indent)
                             .Append(child.Key)
                             .Append('=')
-                            .Append(valueAndProvider.Value)
+                            .Append(value)
                             .Append(" (")
                             .Append(valueAndProvider.Provider)
                             .AppendLine(")");