Placeholder resolution should only be logged at trace-level

---------

Co-authored-by: Bart Koelman <104792814+bart-vmware@users.noreply.github.com>

Author: TimHess

src/Configuration/src/Placeholder/PropertyPlaceHolderHelper.cs

@@ -202,7 +202,7 @@ private static string Substring(StringBuilder builder, int start, int end)
         return builder.ToString()[start..end];
     }
 
-    [LoggerMessage(Level = LogLevel.Debug, Message = "Resolved placeholder '{Placeholder}' to '{Value}'.")]
+    [LoggerMessage(Level = LogLevel.Trace, Message = "Resolved placeholder '{Placeholder}' to '{Value}'.")]
     private partial void LogPlaceholderResolved(string placeholder, string value);
 
     private readonly struct PlaceholderExpression(string key, string? defaultValue) : IEquatable<PlaceholderExpression>

src/Configuration/test/Encryption.Test/DecryptionConfigurationTest.cs

@@ -85,6 +85,34 @@ public void Can_resolve_placeholder_to_decrypted_value()
         configuration["result"].Should().Be("start-SECRET-end");
     }
 
+    [Fact]
+    public void Decrypted_values_in_placeholder_resolution_are_only_logged_at_trace_level()
+    {
+        var decryptor = new ToUpperCaseDecryptor();
+        using var capturingProvider = new CapturingLoggerProvider();
+        using var loggerFactory = new LoggerFactory([capturingProvider]);
+
+        var appSettings = new Dictionary<string, string?>
+        {
+            ["secret"] = "{cipher}classified",
+            ["greeting"] = "hello-${secret}-world"
+        };
+
+        var builder = new ConfigurationBuilder();
+        builder.AddInMemoryCollection(appSettings);
+        builder.AddDecryption(decryptor, loggerFactory);
+        builder.AddPlaceholderResolver(loggerFactory);
+        IConfiguration configuration = builder.Build();
+
+        _ = configuration["greeting"];
+
+        IList<string> logLines = capturingProvider.GetAll();
+        string[] sensitiveLines = [.. logLines.Where(message => message.Contains("CLASSIFIED", StringComparison.Ordinal))];
+
+        sensitiveLines.Should().NotBeEmpty();
+        sensitiveLines.Should().AllSatisfy(message => message.Should().StartWith("TRCE"));
+    }
+
     public void Dispose()
     {
         _loggerFactory.Dispose();