Handle error when pwsh does not exist language agnostic (Azure#41910)

Author: christothes

sdk/identity/Azure.Identity/CHANGELOG.md

@@ -7,6 +7,7 @@
 ### Breaking Changes
 
 ### Bugs Fixed
+- `AzurePowerShellCredential` now handles the case where it falls back to legacy powershell without relying on the error message string.
 
 ### Other Changes
 

sdk/identity/Azure.Identity/src/Credentials/AzurePowerShellCredential.cs

@@ -159,7 +159,7 @@ private async ValueTask<AccessToken> RequestAzurePowerShellAccessTokenAsync(bool
             try
             {
                 output = async ? await processRunner.RunAsync().ConfigureAwait(false) : processRunner.Run();
-                CheckForErrors(output);
+                CheckForErrors(output, processRunner.ExitCode);
                 ValidateResult(output);
             }
             catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)
@@ -168,7 +168,7 @@ private async ValueTask<AccessToken> RequestAzurePowerShellAccessTokenAsync(bool
             }
             catch (InvalidOperationException exception)
             {
-                CheckForErrors(exception.Message);
+                CheckForErrors(exception.Message, processRunner.ExitCode);
                 if (_isChainedCredential)
                 {
                     throw new CredentialUnavailableException($"{AzurePowerShellFailedError} {exception.Message}");
@@ -181,9 +181,10 @@ private async ValueTask<AccessToken> RequestAzurePowerShellAccessTokenAsync(bool
             return DeserializeOutput(output);
         }
 
-        private static void CheckForErrors(string output)
+        private static void CheckForErrors(string output, int exitCode)
         {
-            bool noPowerShell = (output.IndexOf("not found", StringComparison.OrdinalIgnoreCase) != -1 ||
+            int notFoundExitCode = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? 9009 : 127;
+            bool noPowerShell = (exitCode == notFoundExitCode || output.IndexOf("not found", StringComparison.OrdinalIgnoreCase) != -1 ||
                                 output.IndexOf("is not recognized", StringComparison.OrdinalIgnoreCase) != -1) &&
                                 // If the error contains AADSTS, this should be treated as a general error to be bubbled to the user
                                 output.IndexOf("AADSTS", StringComparison.OrdinalIgnoreCase) == -1;
@@ -264,7 +265,7 @@ private void GetFileNameAndArguments(string resource, string tenantId, out strin
             if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
             {
                 fileName = Path.Combine(DefaultWorkingDirWindows, "cmd.exe");
-                argument = $"/d /c \"{powershellExe} \"{commandBase64}\" \"";
+                argument = $"/d /c \"{powershellExe} \"{commandBase64}\" \" & exit";
             }
             else
             {

sdk/identity/Azure.Identity/src/ProcessRunner.cs

@@ -23,6 +23,7 @@ internal sealed class ProcessRunner : IDisposable
         private readonly CancellationTokenSource _timeoutCts;
         private CancellationTokenRegistration _ctRegistration;
         private bool _logPII;
+        public int ExitCode => _process.ExitCode;
 
         public ProcessRunner(IProcess process, TimeSpan timeout, bool logPII, CancellationToken cancellationToken)
         {

sdk/identity/Azure.Identity/tests/AzurePowerShellCredentialsTests.cs

@@ -119,6 +119,7 @@ private static IEnumerable<object[]> FallBackErrorScenarios()
             yield return new object[] { "'pwsh' is not recognized", AzurePowerShellCredential.PowerShellNotInstalledError };
             yield return new object[] { "pwsh: command not found", AzurePowerShellCredential.PowerShellNotInstalledError };
             yield return new object[] { "pwsh: not found", AzurePowerShellCredential.PowerShellNotInstalledError };
+            yield return new object[] { "foo bar", AzurePowerShellCredential.PowerShellNotInstalledError };
         }
 
         [Test]
@@ -127,7 +128,9 @@ public void AuthenticateWithAzurePowerShellCredential_FallBackErrorScenarios(str
         {
             // This will require two processes on Windows and one on other platforms
             // Purposefully stripping out the second process to ensure any attempt to fallback is caught on non-Windows
-            TestProcess[] testProcesses = new TestProcess[] { new TestProcess { Error = errorMessage }, new TestProcess { Error = errorMessage } };
+            int exitCode = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? 9009 : 127;
+
+            TestProcess[] testProcesses = new TestProcess[] { new TestProcess { Error = errorMessage, CodeOnExit = exitCode }, new TestProcess { Error = errorMessage, CodeOnExit = exitCode } };
             if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
                 testProcesses = new TestProcess[] { testProcesses[0] };