Don't register as system proxy or install root cert by default in CI

DevProxy.Tests/ProxyConfigurationCiDefaultsTests.cs

@@ -0,0 +1,95 @@
+// 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 file in the project root for more information.
+
+using DevProxy.Commands;
+using DevProxy.Proxy;
+using Microsoft.Extensions.Configuration;
+using Xunit;
+
+namespace DevProxy.Tests;
+
+public class ProxyConfigurationCiDefaultsTests
+{
+    private static ProxyConfiguration Create(bool isCi, Dictionary<string, string?>? settings = null)
+    {
+        var configurationRoot = new ConfigurationBuilder()
+            .AddInMemoryCollection(settings ?? [])
+            .Build();
+        return new ProxyConfiguration(configurationRoot, isCi);
+    }
+
+    [Fact]
+    public void NotCi_KeepsDefaults()
+    {
+        var config = Create(isCi: false);
+
+        Assert.True(config.AsSystemProxy);
+        Assert.True(config.InstallCert);
+        Assert.False(config.AsSystemProxyDefaultedForCi);
+        Assert.False(config.InstallCertDefaultedForCi);
+    }
+
+    [Fact]
+    public void Ci_NotSetInConfig_DisablesSystemProxyAndCertInstall()
+    {
+        var config = Create(isCi: true);
+
+        Assert.False(config.AsSystemProxy);
+        Assert.False(config.InstallCert);
+        Assert.True(config.AsSystemProxyDefaultedForCi);
+        Assert.True(config.InstallCertDefaultedForCi);
+    }
+
+    [Theory]
+    [InlineData("true", true)]
+    [InlineData("false", false)]
+    public void Ci_SetInConfig_KeepsConfiguredValues(string value, bool expected)
+    {
+        var config = Create(isCi: true, new()
+        {
+            ["asSystemProxy"] = value,
+            ["installCert"] = value,
+        });
+
+        Assert.Equal(expected, config.AsSystemProxy);
+        Assert.Equal(expected, config.InstallCert);
+        Assert.False(config.AsSystemProxyDefaultedForCi);
+        Assert.False(config.InstallCertDefaultedForCi);
+    }
+
+    [Fact]
+    public void Ci_OnlyAsSystemProxyInConfig_DefaultsInstallCertOnly()
+    {
+        var config = Create(isCi: true, new() { ["asSystemProxy"] = "true" });
+
+        Assert.True(config.AsSystemProxy);
+        Assert.False(config.InstallCert);
+        Assert.False(config.AsSystemProxyDefaultedForCi);
+        Assert.True(config.InstallCertDefaultedForCi);
+    }
+
+    [Fact]
+    public void ShouldLogCiDefaults_NotCi_ReturnsFalse()
+    {
+        Assert.False(DevProxyCommand.ShouldLogCiDefaults(Create(isCi: false), null, null));
+    }
+
+    [Fact]
+    public void ShouldLogCiDefaults_CiDefaultsApplied_ReturnsTrue()
+    {
+        Assert.True(DevProxyCommand.ShouldLogCiDefaults(Create(isCi: true), null, null));
+    }
+
+    [Fact]
+    public void ShouldLogCiDefaults_OneOverriddenOnCommandLine_ReturnsTrue()
+    {
+        Assert.True(DevProxyCommand.ShouldLogCiDefaults(Create(isCi: true), true, null));
+    }
+
+    [Fact]
+    public void ShouldLogCiDefaults_BothOverriddenOnCommandLine_ReturnsFalse()
+    {
+        Assert.False(DevProxyCommand.ShouldLogCiDefaults(Create(isCi: true), true, true));
+    }
+}

DevProxy/Commands/DevProxyCommand.cs

@@ -490,8 +490,8 @@ private void ConfigureCommand(DevProxyConfigOptions configOptions)
         {
             try
             {
-                var asSystemProxy = input.GetValue(asSystemProxyOption) ?? true;
-                var installCert = input.GetValue(installCertOption) ?? true;
+                var asSystemProxy = input.GetValue(asSystemProxyOption) ?? _proxyConfiguration.AsSystemProxy;
+                var installCert = input.GetValue(installCertOption) ?? _proxyConfiguration.InstallCert;
                 if (asSystemProxy && !installCert)
                 {
                     input.AddError($"Requires option '{AsSystemProxyOptionName}' to be 'false'");
@@ -746,6 +746,7 @@ private void ConfigureFromOptions(ParseResult parseResult)
         {
             _proxyConfiguration.InstallCert = installCert.Value;
         }
+        LogCiDefaults(asSystemProxy, installCert);
         var timeout = parseResult.GetValueOrDefault<long?>(TimeoutOptionName);
         if (timeout is not null)
         {
@@ -771,6 +772,26 @@ private void ConfigureFromOptions(ParseResult parseResult)
         }
     }
 
+    private void LogCiDefaults(bool? asSystemProxyOption, bool? installCertOption)
+    {
+        if (_proxyConfiguration is not ProxyConfiguration proxyConfiguration ||
+            !ShouldLogCiDefaults(proxyConfiguration, asSystemProxyOption, installCertOption))
+        {
+            return;
+        }
+
+        _logger.LogInformation(
+            "CI environment detected. Using asSystemProxy: {AsSystemProxy}, installCert: {InstallCert}. To change, use {AsSystemProxyOption} and {InstallCertOption} or set asSystemProxy and installCert in the config file.",
+            proxyConfiguration.AsSystemProxy.ToString().ToLowerInvariant(),
+            proxyConfiguration.InstallCert.ToString().ToLowerInvariant(),
+            AsSystemProxyOptionName,
+            InstallCertOptionName);
+    }
+
+    internal static bool ShouldLogCiDefaults(ProxyConfiguration proxyConfiguration, bool? asSystemProxyOption, bool? installCertOption) =>
+        (proxyConfiguration.AsSystemProxyDefaultedForCi && asSystemProxyOption is null) ||
+        (proxyConfiguration.InstallCertDefaultedForCi && installCertOption is null);
+
     private async Task CheckForNewVersionAsync()
     {
         var newReleaseInfo = await _updateNotification.CheckForNewVersionAsync(_proxyConfiguration.NewVersionNotification);

DevProxy/Proxy/ProxyConfiguration.cs

@@ -53,10 +53,41 @@ public string ConfigFile
     public IEnumerable<string> WatchProcessNames { get; set; } = [];
     public bool WatchProcessTree { get; set; }
 
-    public ProxyConfiguration(IConfigurationRoot configurationRoot)
+    // True when the value wasn't set in the config file and was turned off
+    // because Dev Proxy is running in CI.
+    internal bool AsSystemProxyDefaultedForCi { get; private set; }
+    internal bool InstallCertDefaultedForCi { get; private set; }
+
+    internal static bool IsCi => Environment.GetEnvironmentVariable("CI") is not null;
+
+    public ProxyConfiguration(IConfigurationRoot configurationRoot) : this(configurationRoot, IsCi)
+    {
+    }
+
+    internal ProxyConfiguration(IConfigurationRoot configurationRoot, bool isCi)
     {
         _configurationRoot = configurationRoot;
         _configurationRoot.Bind(this);
+        if (isCi)
+        {
+            ApplyCiDefaults(_configurationRoot);
+        }
+    }
+
+    // In CI, don't change machine-wide state (system proxy, trusted root
+    // certificates) unless the config file explicitly asks for it.
+    private void ApplyCiDefaults(IConfiguration configuration)
+    {
+        if (configuration[nameof(AsSystemProxy)] is null)
+        {
+            AsSystemProxy = false;
+            AsSystemProxyDefaultedForCi = true;
+        }
+        if (configuration[nameof(InstallCert)] is null)
+        {
+            InstallCert = false;
+            InstallCertDefaultedForCi = true;
+        }
     }
 
     internal static string GetConfigFilePath(IConfigurationRoot configurationRoot)

skills/dev-proxy/references/ci-cd-integration.md

@@ -4,6 +4,8 @@ Dev Proxy runs headlessly in CI/CD pipelines to automate API testing — catchin
 
 With Dev Proxy 3.3.1 or later, every management API request requires a bearer token. Set `CI=true` in the proxy process to suppress automatic token output, and retrieve credentials explicitly with `devproxy api token`. Keep shell tracing disabled around credentials. For multiple instances, add `--pid <PID>` and use the actual API URL from `devproxy status`.
 
+When `CI` is set, Dev Proxy doesn't register itself as the system proxy or install its root certificate, unless you set `asSystemProxy` or `installCert` in the config file or pass `--as-system-proxy` or `--install-cert`. Point your app at Dev Proxy with `HTTPS_PROXY`/`HTTP_PROXY` and trust the root certificate as shown below.
+
 Use action versions that support the authenticated API. For integrations that have not yet added bearer authentication, use the CLI and authenticated HTTP examples below.
 
 ## GitHub Actions (Recommended)

skills/dev-proxy/references/configuration.md

@@ -136,7 +136,8 @@ Plugin-specific override:
 | `watchPids` | — | `--watch-pids` | Only intercept from these PIDs |
 | `watchProcessNames` | — | `--watch-process-names` | Only intercept from these processes |
 | `watchProcessTree` | — | `--watch-process-tree` | Also intercept descendants of watched processes |
-| `asSystemProxy` | `true` | `--as-system-proxy` | Register as system proxy |
+| `asSystemProxy` | `true` (`false` when `CI` is set) | `--as-system-proxy` | Register as system proxy |
+| `installCert` | `true` (`false` when `CI` is set) | `--install-cert` | Install and trust the root certificate |
 | — | off | `--detach` | Run in detached (background) mode |
 | — | `text` | `--output` | Output format: `text` or `json` |