How to schedule a Task to be executed under the Users group from a Windows C# Service?

[scornz]

I have a WPF application that I am attempting to start upon every logon of a user. The only issue is that the specified group is "SYSTEM" since I am creating the task from a service application. So, when the application is started, the UI will never appear (as expected). If I go into the Task Scheduler UI and manually change the user/group to "Users", the WPF application opens and the UI is visible. This is the current script:

// Create a new task definition for the local machine and assign properties
TaskDefinition td = TaskService.Instance.NewTask();
td.RegistrationInfo.Description = "Launch test-login";
//td.Settings.RunOnlyIfLoggedOn = true;
#pragma warning disable CA1416 // Validate platform compatibility
string userId = System.Security.Principal.WindowsIdentity.GetCurrent().Name;
#pragma warning restore CA1416 // Validate platform compatibility

td.Principal.UserId = userId;
td.Principal.LogonType = TaskLogonType.InteractiveToken;

LogonTrigger lt = new LogonTrigger();
td.Triggers.Add(lt);

string executePath = Path.GetDirectoryName(Environment.GetCommandLineArgs()[0]) + "\\login.exe";
td.Actions.Add(executePath);

// Register the task in the root folder of the local machine
TaskService.Instance.RootFolder.RegisterTaskDefinition("login-start", td, TaskCreation.CreateOrUpdate, userId, logonType: TaskLogonType.InteractiveToken);

I understand why the above code won't work, since GetCurrent() will simply return "SYSTEM" since this code is in a service. Any advice on how to solve this?

[dahall]

You're on the right track. Do not set the td.Principal properties. Then, in the RegisterTaskDefinition call, do the following:

TaskService.Instance.RootFolder.RegisterTaskDefinition("westlightlogin-start", td, TaskCreation.CreateOrUpdate, "YourDomain\\GroupAcct", null, TaskLogonType.Group);

[scornz]

Ah, okay. That makes sense. In order to make this universally supported, how would I get the domain name of the "Users" group? This may be a stupid question, but it just seems quite difficult from a windows service.

[dahall]

Try "BUILTIN\Authenticated Users". I think that's the format to get the special group for all users.

[scornz]

Removing the td.Principal properties and modifying the RegisterTaskDefinition call works wonders. The group is set to "Authenticated Users" and the WPF application UI is now visible. Here is what the call ended up being:

// Register the task in the root folder of the local machine
TaskService.Instance.RootFolder.RegisterTaskDefinition("login-start", td, TaskCreation.CreateOrUpdate, "Authenticated Users", null, TaskLogonType.Group);