How to run a non-interactive process as another user in a Windows Service using C#? [proof-of-concept]

Non-Interactive-Process-Windows-Service.cs

/**
* This application converts a text message to uppercase by spawning a child process as another user and saves it to a file.
*
* Usage: app.exe MESSAGE FILE_PATH
* or
* Usage: app.exe DOMAIN USERNAME PASSWORD MESSAGE FILE_PATH
*
*
* Setup instructions:
*
* 1. Open secpol.msc
* 2. Navigate to 'Local Policies' > 'User Rights Assignment' > 'Log on as a service'.
* 3. Add your account and click the 'OK' button.
* 4. Compile this file as a console application.
* 5. Open a PowerShell console as administrator.
* 6. PS C:\> New-Service ServiceTest "CONSOLE_EXE_PATH MESSAGE FILE_PATH" -Credential YOUR_DOMAIN\YOUR_ACCOUNT
* 7. PS C:\> Start-Service ServiceTest
* 8. Verify that the file is created with the message in uppercase.
* 10. Delete the file.
* 11. PS C:\> Stop-Service ServiceTest
* 12. PS C:\> sc.exe delete ServiceTest
* 13. PS C:\> New-Service ServiceTest "CONSOLE_EXE_PATH YOUR_DOMAIN ANOTHER_ACCOUNT_USERNAME PASSWORD MESSAGE FILE_PATH" -Credential YOUR_DOMAIN\YOUR_ACCOUNT
* 14. Ensure the YOUR_DOMAIN\ANOTHER_ACCOUNT_USERNAME has access to the folder where CONSOLE_EXE_PATH is located.
* 15. PS C:\> Start-Service ServiceTest
* 16. Verify that the file is not created.
* 17. Open eventvwr
* 18. Verify that a { "Log Name": "System", "Source": "Application Popup", "EventId": 26, "Data": ["CONSOLE_EXE - Application Error", "The application was unable to start correctly (0xc0000142). Click OK to close the application."] } event is registered.
* 19. PS C:\> Stop-Service ServiceTest
* 20. PS C:\> sc.exe delete ServiceTest
*/

namespace ServiceTest
{
    using System;
    using System.Diagnostics;
    using System.IO;
    using System.Net;
    using System.ServiceProcess;
    using System.Text;
    using System.Threading;

    internal sealed class Program : ServiceBase
    {
        private const string ChildIndicator = "079a9ab7-e4b8-4192-9dc7-dc7b93ec9376";

        private readonly string[] args;
        private readonly ManualResetEventSlim processDone = new ManualResetEventSlim();

        private Program(string[] args)
        {
            this.args = args;
        }

        public static void Main(string[] args)
        {
            if (Environment.UserInteractive || Program.IsChildProcess(args))
            {
                var p = new Program(args);
                p.OnStart(null);
                p.OnStop();
            }
            else
            {
                ServiceBase.Run(new Program(args));
            }
        }

        protected override void OnStart(string[] notUsed)
        {
            if (Program.IsChildProcess(this.args))
            {
                Console.WriteLine("handshake");
                var input = Console.In.ReadToEnd();
                if (input != null)
                {
                    Console.WriteLine(input.ToUpper());
                }

                this.processDone.Set();
            }
            else if (this.args.Length == 2 || this.args.Length == 5)
            {
                var credentials = this.args.Length == 5 ? new NetworkCredential(this.args[1], this.args[2], this.args[0]) : null;
                var message = this.args.Length == 5 ? this.args[3] : this.args[0];
                var outputFile = this.args.Length == 5 ? this.args[4] : this.args[1];

                // Create process.
                var process = new Process
                {
                    EnableRaisingEvents = true,
                    StartInfo =
                    {
                        FileName = Process.GetCurrentProcess().MainModule.FileName,
                        Arguments = Program.ChildIndicator,
                        CreateNoWindow = true,
                        RedirectStandardError = true,
                        RedirectStandardInput = true,
                        RedirectStandardOutput = true,
                        UseShellExecute = false,
                        WorkingDirectory = @"C:\"
                    }
                };

                if (credentials != null)
                {
                    process.StartInfo.Domain = credentials.Domain;
                    process.StartInfo.UserName = credentials.UserName;
                    process.StartInfo.Password = credentials.SecurePassword;
                }

                var error = new StringBuilder();
                var errorWaitHandle = new ManualResetEventSlim();
                process.ErrorDataReceived += (s, e) =>
                {
                    if (e.Data != null)
                    {
                        error.AppendLine(e.Data);
                    }
                    else
                    {
                        errorWaitHandle.Set();
                    }
                };

                var output = new StringBuilder();
                var outputWaitHandle = new ManualResetEventSlim();
                process.OutputDataReceived += (s, e) =>
                {
                    if (e.Data == "handshake")
                    {
                        process.StandardInput.Write(message);
                        process.StandardInput.Close();
                    }
                    else if (e.Data != null)
                    {
                        output.AppendLine(e.Data);
                    }
                    else
                    {
                        outputWaitHandle.Set();
                    }
                };

                process.Exited += (s, e) =>
                {
                    try
                    {
                        errorWaitHandle.Wait();
                        outputWaitHandle.Wait();

                        if (error.Length > 0)
                        {
                            File.WriteAllText(outputFile, string.Format("Child process completed with an error: {0}", error));
                        }
                        else if (output.Length > 0)
                        {
                            File.WriteAllText(outputFile, output.ToString());
                        }
                    }
                    finally
                    {
                        process.Dispose();

                        this.processDone.Set();
                    }
                };

                process.Start();
                process.BeginErrorReadLine();
                process.BeginOutputReadLine();
            }
            else
            {
                using (var currentProcess = Process.GetCurrentProcess())
                {
                    Console.WriteLine("Usage:");
                    Console.WriteLine("{0} <msg> <path_to_output_file>", currentProcess.MainModule.ModuleName);
                    Console.WriteLine("{0} <domain> <username> <password> <msg> <path_to_output_file>", currentProcess.MainModule.ModuleName);

                    this.processDone.Set();
                }
            }
        }

        protected override void OnStop()
        {
            this.processDone.Wait();
        }

        private static bool IsChildProcess(string[] args)
        {
            return args.Length == 1 && args[0] == Program.ChildIndicator;
        }
    }
}