Stop logging stdio transport environment variables (#1538)

Author: Copilot

src/ModelContextProtocol.Core/Client/StdioClientTransport.cs

@@ -126,9 +126,8 @@ public async Task<ITransport> ConnectAsync(CancellationToken cancellationToken =
 
             if (logger.IsEnabled(LogLevel.Trace))
             {
-                LogCreateProcessForTransportSensitive(logger, endpointName, _options.Command,
+                LogCreateProcessForTransportDetailed(logger, endpointName, _options.Command,
                     startInfo.Arguments,
-                    string.Join(", ", startInfo.Environment.Select(kvp => $"{kvp.Key}={kvp.Value}")),
                     startInfo.WorkingDirectory);
             }
             else
@@ -300,8 +299,8 @@ private static string EscapeArgumentString(string argument) =>
     [LoggerMessage(Level = LogLevel.Information, Message = "{EndpointName} starting server process. Command: '{Command}'.")]
     private static partial void LogCreateProcessForTransport(ILogger logger, string endpointName, string command);
 
-    [LoggerMessage(Level = LogLevel.Trace, Message = "{EndpointName} starting server process. Command: '{Command}', Arguments: {Arguments}, Environment: {Environment}, Working directory: {WorkingDirectory}.")]
-    private static partial void LogCreateProcessForTransportSensitive(ILogger logger, string endpointName, string command, string? arguments, string environment, string workingDirectory);
+    [LoggerMessage(Level = LogLevel.Trace, Message = "{EndpointName} starting server process. Command: '{Command}', Arguments: {Arguments}, Working directory: {WorkingDirectory}.")]
+    private static partial void LogCreateProcessForTransportDetailed(ILogger logger, string endpointName, string command, string? arguments, string workingDirectory);
 
     [LoggerMessage(Level = LogLevel.Warning, Message = "{EndpointName} failed to start server process.")]
     private static partial void LogTransportProcessStartFailed(ILogger logger, string endpointName);

tests/ModelContextProtocol.Tests/Transport/StdioClientTransportTests.cs

@@ -1,4 +1,5 @@
-using ModelContextProtocol.Client;
+using Microsoft.Extensions.Logging;
+using ModelContextProtocol.Client;
 using ModelContextProtocol.Protocol;
 using ModelContextProtocol.Tests.Utils;
 using System.IO.Pipelines;
@@ -12,6 +13,42 @@ public class StdioClientTransportTests(ITestOutputHelper testOutputHelper) : Log
 {
     public static bool IsStdErrCallbackSupported => !PlatformDetection.IsMonoRuntime;
 
+    [Fact]
+    public async Task ConnectAsync_DoesNotLogEnvironmentVariablesAtTrace()
+    {
+        string secretName = $"MCP_TEST_SECRET_{Guid.NewGuid():N}";
+        string secretValue = $"secret-{Guid.NewGuid():N}";
+
+        using var loggerFactory = Microsoft.Extensions.Logging.LoggerFactory.Create(builder =>
+        {
+            builder.AddProvider(MockLoggerProvider);
+            builder.SetMinimumLevel(LogLevel.Trace);
+        });
+
+        StdioClientTransport transport = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ?
+            new(new()
+            {
+                Command = "cmd.exe",
+                Arguments = ["/c", "exit /b 0"],
+                EnvironmentVariables = new Dictionary<string, string?> { [secretName] = secretValue },
+            }, loggerFactory) :
+            new(new()
+            {
+                Command = "sh",
+                Arguments = ["-c", "exit 0"],
+                EnvironmentVariables = new Dictionary<string, string?> { [secretName] = secretValue },
+            }, loggerFactory);
+
+        await using var _ = await transport.ConnectAsync(TestContext.Current.CancellationToken);
+
+        Assert.Contains(MockLoggerProvider.LogMessages, log =>
+            log.LogLevel == LogLevel.Trace &&
+            log.Message.Contains("starting server process", StringComparison.Ordinal));
+        Assert.DoesNotContain(MockLoggerProvider.LogMessages, log =>
+            log.Message.Contains(secretName, StringComparison.Ordinal) ||
+            log.Message.Contains(secretValue, StringComparison.Ordinal));
+    }
+
     [Fact]
     public async Task CreateAsync_ValidProcessInvalidServer_Throws()
     {