Add flag to enable running tests with Fiddler (Azure#27392)

* Add flag to enable running tests with Fiddler

* PR fb

* Fix readme

* fix

* one more

Author: JoshLove-msft

eng/nunit.runsettings

@@ -16,6 +16,9 @@
 
         <!-- Change the test mode -->
         <!-- <Parameter name="TestMode" value="Record" /> -->
+        
+        <!-- Enable running Fiddler -->
+        <!-- <Parameter name="EnableFiddler" value="true" /> -->
     </TestRunParameters>
 
 </RunSettings>

sdk/core/Azure.Core.TestFramework/README.md

@@ -302,6 +302,8 @@ You can use `if (Mode == RecordingMode.Playback) { ... }` to change behavior for
 
 You can use `using (Recording.DisableRecording()) { ... }` to disable recording in the code block (useful for polling methods)
 
+In order to enable testing with Fiddler, you can either set the  `AZURE_ENABLE_FIDDLER` environment variable or the `EnableFiddler` [runsetting](https://github.com/Azure/azure-sdk-for-net/blob/main/eng/nunit.runsettings) parameter to `true`.
+
 ## Support multi service version testing
 
 To enable multi-version testing, add the `ClientTestFixture` attribute listing to all the service versions to the test class itself or a base class:

sdk/core/Azure.Core.TestFramework/src/ProxyTransport.cs

@@ -19,18 +19,30 @@ public class ProxyTransport : HttpPipelineTransport
         private readonly TestProxy _proxy;
         private readonly bool _isWebRequestTransport;
 
-        private static readonly RemoteCertificateValidationCallback ServerCertificateCustomValidationCallback =
-            (_, certificate, _, _) => certificate.Issuer == TestProxy.DevCertIssuer;
+        private const string DevCertIssuer = "CN=localhost";
+        private const string FiddlerCertIssuer = "CN=DO_NOT_TRUST_FiddlerRoot, O=DO_NOT_TRUST, OU=Created by http://www.fiddler2.com";
+
+        private readonly RemoteCertificateValidationCallback _serverCertificateCustomValidationCallback;
 
         private readonly Func<EntryRecordModel> _filter;
+        private readonly string _proxyHost;
+
+        private static bool s_useFiddler => TestEnvironment.EnableFiddler;
 
         public ProxyTransport(TestProxy proxy, HttpPipelineTransport transport, TestRecording recording, Func<EntryRecordModel> filter)
         {
+            _recording = recording;
+            _proxy = proxy;
+            _filter = filter;
+
+            string certIssuer = s_useFiddler ? FiddlerCertIssuer : DevCertIssuer;
+            _proxyHost = s_useFiddler ? "localhost.fiddler" : TestProxy.IpAddress;
+
             if (transport is HttpClientTransport)
             {
                 var handler = new HttpClientHandler
                 {
-                    ServerCertificateCustomValidationCallback = (_, certificate, _, _) => certificate.Issuer == TestProxy.DevCertIssuer
+                    ServerCertificateCustomValidationCallback = (_, certificate, _, _) => certificate.Issuer == certIssuer
                 };
                 _innerTransport = new HttpClientTransport(handler);
             }
@@ -39,10 +51,8 @@ public ProxyTransport(TestProxy proxy, HttpPipelineTransport transport, TestReco
             {
                 _isWebRequestTransport = true;
                 _innerTransport = transport;
+                _serverCertificateCustomValidationCallback = (_, certificate, _, _) => certificate.Issuer == certIssuer;
             }
-            _recording = recording;
-            _proxy = proxy;
-            _filter = filter;
         }
 
         public override void Process(HttpMessage message) =>
@@ -80,7 +90,7 @@ private async Task ProcessAsyncInternalAsync(HttpMessage message, bool async)
 
                 if (_isWebRequestTransport)
                 {
-                    ServicePointManager.ServerCertificateValidationCallback -= ServerCertificateCustomValidationCallback;
+                    ServicePointManager.ServerCertificateValidationCallback -= _serverCertificateCustomValidationCallback;
                 }
             }
         }
@@ -159,13 +169,12 @@ private void RedirectToTestProxy(HttpMessage message)
             };
             request.Headers.SetValue("x-recording-upstream-base-uri", baseUri.ToString());
 
-            // for some reason using localhost instead of the ip address causes slowness when combined with SSL callback being specified
-            request.Uri.Host = TestProxy.IpAddress;
+            request.Uri.Host = _proxyHost;
             request.Uri.Port = request.Uri.Scheme == "https" ? _proxy.ProxyPortHttps.Value : _proxy.ProxyPortHttp.Value;
 
             if (_isWebRequestTransport)
             {
-                ServicePointManager.ServerCertificateValidationCallback += ServerCertificateCustomValidationCallback;
+                ServicePointManager.ServerCertificateValidationCallback += _serverCertificateCustomValidationCallback;
             }
         }
     }

sdk/core/Azure.Core.TestFramework/src/TestEnvironment.cs

@@ -632,6 +632,22 @@ internal static bool GlobalDisableAutoRecording
             }
         }
 
+        /// <summary>
+        /// Determines whether to enable the test framework to proxy traffic through fiddler.
+        /// </summary>
+        internal static bool EnableFiddler
+        {
+            get
+            {
+                string switchString = TestContext.Parameters["EnableFiddler"] ??
+                                      Environment.GetEnvironmentVariable("AZURE_ENABLE_FIDDLER");
+
+                bool.TryParse(switchString, out bool enableFiddler);
+
+                return enableFiddler;
+            }
+        }
+
         private void BootStrapTestResources()
         {
             lock (s_syncLock)

sdk/core/Azure.Core.TestFramework/src/TestProxy.cs

@@ -24,8 +24,7 @@ public class TestProxy
     {
         private static readonly string s_dotNetExe;
 
-        public const string DevCertIssuer = "CN=localhost";
-
+        // for some reason using localhost instead of the ip address causes slowness when combined with SSL callback being specified
         public const string IpAddress = "127.0.0.1";
 
         public int? ProxyPortHttp => _proxyPortHttp;