Update Az CLI Cred flow to redirect stdin (Azure#49582)

Author: g2vinay

sdk/identity/Azure.Identity/CHANGELOG.md

@@ -7,6 +7,7 @@
 ### Breaking Changes
 
 ### Bugs Fixed
+- Fixed an issue where Azure CLI credential could hang or delay due to I/O contention when standard input/output was shared with the host process ([#49582](https://github.com/Azure/azure-sdk-for-net/pull/49582)).
 
 ### Other Changes
 

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

@@ -132,7 +132,7 @@ private async ValueTask<AccessToken> RequestCliAccessTokenAsync(bool async, Toke
 
             GetFileNameAndArguments(resource, tenantId, Subscription, out string fileName, out string argument);
             ProcessStartInfo processStartInfo = GetAzureCliProcessStartInfo(fileName, argument);
-            using var processRunner = new ProcessRunner(_processService.Create(processStartInfo), ProcessTimeout, _logPII, cancellationToken);
+            using var processRunner = new ProcessRunner(_processService.Create(processStartInfo), ProcessTimeout, _logPII, redirectStandardInput: true, cancellationToken);
 
             string output;
             try

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

@@ -3,6 +3,7 @@
 
 using System;
 using System.Diagnostics;
+using System.IO;
 
 namespace Azure.Identity
 {
@@ -20,5 +21,6 @@ internal interface IProcess : IDisposable
         void Kill();
         void BeginOutputReadLine();
         void BeginErrorReadLine();
+        StreamWriter StandardInput { get; }
     }
 }

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

@@ -18,6 +18,7 @@ internal sealed class ProcessRunner : IDisposable
         private readonly TaskCompletionSource<ICollection<string>> _errorTcs;
         private readonly ICollection<string> _outputData;
         private readonly ICollection<string> _errorData;
+        private readonly bool _redirectStandardInput;
 
         private readonly CancellationToken _cancellationToken;
         private readonly CancellationTokenSource _timeoutCts;
@@ -26,10 +27,15 @@ internal sealed class ProcessRunner : IDisposable
         public int ExitCode => _process.ExitCode;
 
         public ProcessRunner(IProcess process, TimeSpan timeout, bool logPII, CancellationToken cancellationToken)
+            : this(process, timeout, logPII, false, cancellationToken)
+        { }
+
+        public ProcessRunner(IProcess process, TimeSpan timeout, bool logPII, bool redirectStandardInput, CancellationToken cancellationToken)
         {
             _logPII = logPII;
             _process = process;
             _timeout = timeout;
+            _redirectStandardInput = redirectStandardInput;
 
             if (_logPII)
             {
@@ -77,6 +83,7 @@ private void StartProcess()
             _process.StartInfo.UseShellExecute = false;
             _process.StartInfo.RedirectStandardOutput = true;
             _process.StartInfo.RedirectStandardError = true;
+            _process.StartInfo.RedirectStandardInput = _redirectStandardInput;
 
             _process.OutputDataReceived += (sender, args) => OnDataReceived(args, _outputData, _outputTcs);
             _process.ErrorDataReceived += (sender, args) => OnDataReceived(args, _errorData, _errorTcs);
@@ -92,6 +99,21 @@ private void StartProcess()
             _process.BeginOutputReadLine();
             _process.BeginErrorReadLine();
             _ctRegistration = _cancellationToken.Register(HandleCancel, false);
+
+            if (_redirectStandardInput)
+            {
+                try
+                {
+                    _process.StandardInput.Close();
+                }
+                catch (Exception ex)
+                {
+                    if (_logPII)
+                    {
+                        AzureIdentityEventSource.Singleton.ProcessRunnerError($"Failed to close StandardInput: {ex}");
+                    }
+                }
+            }
         }
 
         private async ValueTask HandleExitAsync()

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

@@ -36,6 +36,7 @@ public ProcessStartInfo StartInfo
                 get => _process.StartInfo;
                 set => _process.StartInfo = value;
             }
+            public StreamWriter StandardInput => _process.StandardInput;
 
             public event EventHandler Exited
             {

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

@@ -3,6 +3,7 @@
 
 using System;
 using System.Diagnostics;
+using System.IO;
 using System.Linq.Expressions;
 using System.Reflection;
 using System.Threading;
@@ -71,6 +72,8 @@ public int ExitCode
             }
         }
 
+        public StreamWriter StandardInput => throw new NotImplementedException();
+
         public event EventHandler Exited;
         public event EventHandler Started;
         public event DataReceivedEventHandler OutputDataReceived;