This is how you can query the active user from a script running under other credentials

About Querying Users From Background Scripts.md

Someone on the PowerShell Discord asked about sending a message box to the current user on a computer.

This method should work to query the user for a choice (with an optional timeout) or simply notify them of something, whether the script is being run by the user or by an administrator in a remote PowerShell session, or from system, etc.

It's not thoroughly tested (as with most of what I put on gists), but it does work.

Here's some examples:

Show-RemoteDesktopMessage -Title "Test Message" -Message "This is a test message."

switch (Get-RemoteDesktopResponse -Title "Problem found" -Message "Should we delete the problem file?" -Style "BUTTON_YESNO,ICON_EXCLAMATION") {

    "Yes" { "Deleting the file" }
    "No" { "Leaving the problem for the user to deal with" }
    default { "User did not respond" }
}

Maybe I'll do more later.

RemoteDesktop.psm1

# Send-MessageBox.ps1 with Logging
param(
    # Set up logging
    $logFile = "$($PSScriptRoot)\ShowMessage.log"
)

filter Write-LogMessage {
    param(
        [Parameter(ValueFromRemainingArguments, ValueFromPipeline, Position = 0)]
        [string[]]$Message,

        [switch]$WriteHost
    )
    $Message = "$([DateTime]::Now.ToString("yyyy-MM-dd HH:mm:ss zzz")) $Message"
    $Message | Out-File -Append -FilePath $logFile
    if ($WriteHost) {
        Write-Host $Message
    }
}

# TODO: Should this use WTSEnumerateSessions instead?
function Get-RDSession {
    [CmdletBinding()]
    param(
        [string]$Username
    )
    # Find the session id of the active session by parsing the output of `qwinsta`
    $sessions = (qwinsta) -replace '\s+', ' '
    | Select-String -Pattern "^\s*(?<name>\S+)\s+(?<user>\S+)?\s*(?<id>\d+)\s+(?<state>\S+)"
    | ForEach-Object {
        $props = @{}
        $_.Matches.Groups
        | Where-Object Name -NE 0
        | ForEach-Object { $props[$_.Name] = $_.Value }
        [PSCustomObject]$props
    }
    Write-LogMessage "Qwinsta sessions:"
    $sessions | Out-String -Stream | Write-LogMessage

    if ($Username) {
        $sessions | Where-Object { $_.User -eq $Username }
    } else {
        $sessions | Where-Object { $_.State -eq "Active" }
    }
}


# Start logging
Write-LogMessage "Script started. Logging to $logFile"

# Define the WTS API using C# within PowerShell
if ("RemoteDesktop" -as [type]) {
    Write-LogMessage "C# type already exists in PowerShell."
} else {
    Add-Type @"
using System;
using System.Runtime.InteropServices;
using System.Text;

[Flags]
public enum MessageBoxType : uint {
    // The message box contains three push buttons: Abort, Retry, and Ignore.
    BUTTON_ABORTRETRYIGNORE = (uint)0x00000002L,

    // The message box contains three push buttons: Cancel, Try Again, Continue. Use this message box type instead of MB_ABORTRETRYIGNORE. =
    BUTTON_CANCELTRYCONTINUE = (uint)0x00000006L,

    // Adds a Help button to the message box. When the user clicks the Help button or presses F1, the system sends a WM_HELP message to the owner.
    BUTTON_HELP = (uint)0x00004000L,

    // The message box contains one push button: OK. This is the default.
    BUTTON_OK = (uint)0x00000000L,

    // The message box contains two push buttons: OK and Cancel.
    BUTTON_OKCANCEL = (uint)0x00000001L,

    // The message box contains two push buttons: Retry and Cancel.
    BUTTON_RETRYCANCEL = (uint)0x00000005L,

    // The message box contains two push buttons: Yes and No.
    BUTTON_YESNO = (uint)0x00000004L,

    // The message box contains three push buttons: Yes, No, and Cancel.
    BUTTON_YESNOCANCEL = (uint)0x00000003L,

    // ### To add an icon, specify one of the following values.

    // An exclamation-point icon appears in the message box.
    ICON_EXCLAMATION = (uint)0x00000030L,

    // An icon consisting of a lowercase letter i in a circle appears in the message box.
    ICON_INFORMATION = (uint)0x00000040L,

    // A question-mark icon appears in the message box.
    // The question-mark message icon is no longer recommended
    // because it does not clearly represent a specific type of message
    // and because the phrasing of a message as a question could apply to any message type.
    // additionally, users can confuse the message symbol question mark with Help information.
    // Therefore, do not use this question mark message symbol in your message boxes.
    // The system continues to support its inclusion only for backward compatibility.
    ICON_QUESTION = (uint)0x00000020L,

    // A stop-sign icon appears in the message box.
    ICON_STOP = (uint)0x00000010L,

    // ### To indicate the default button, specify one of the following values.

    // The first button is the default button. This is the default.
    DEFAULT_BUTTON1 = (uint)0x00000000L,

    // The second button is the default button.
    DEFAULT_BUTTON2 = (uint)0x00000100L,

    // The third button is the default button.
    DEFAULT_BUTTON3 = (uint)0x00000200L,

    // The fourth button is the default button.
    DEFAULT_BUTTON4 = (uint)0x00000300L,

    // ## Miscaellaneous Options

    // Same as desktop of the interactive window station. For more information, see Window Stations.
    // if the current input desktop is not the default desktop,
    //  MessageBox does not return until the user switches to the default desktop.
    MB_DEFAULT_DESKTOP_ONLY = (uint)0x00020000L,

    // The text is right-justified.
    MB_RIGHT = (uint)0x00080000L,

    // Displays message and caption text using right-to-left reading order on Hebrew and Arabic systems.
    MB_RTLREADING = (uint)0x00100000L,

    // The message box becomes the foreground window. Internally, the system calls the SetForegroundWindow function for the message box.
    MB_SETFOREGROUND = (uint)0x00010000L,

    // The message box is created with the WS_EX_TOPMOST window style.
    MB_TOPMOST = (uint)0x00040000L,

    // The caller is a service notifying the user of an event. The function displays a message box on the current active desktop, even if there is no user logged on to the computer.
    MB_SERVICE_NOTIFICATION = (uint)0x00200000L

}

public enum MessageBoxResult : int {
    // The OK button was selected.
    Ok = 1,

    // The Cancel button was selected.
    Cancel = 2,

    // The Abort button was selected.
    Abort = 3,

    // The Retry button was selected.
    Retry = 4,

    // The Ignore button was selected.
    Ignore = 5,

    // The Yes button was selected.
    Yes = 6,

    // The No button was selected.
    No = 7,

    // The Try Again button was selected.
    TryAgain = 10,

    // The Continue button was selected.
    Continue = 11,

    // The wait flag wasn't specified so we don't know the result.
    NoWait = 32001,

    // The message box timed out without a response from the user
    Timeout = 32000,

    // The message box call failed
    Failed = 64000
}


public class RemoteDesktop
{
    public static MessageBoxResult QueryMessage(int sessionId, string title, string message, MessageBoxType style = MessageBoxType.BUTTON_YESNO, int timeout = 0)
    {
        MessageBoxResult Response = MessageBoxResult.Failed;
        if (WTSSendMessage(IntPtr.Zero, sessionId, title, Encoding.Unicode.GetByteCount(title), message, Encoding.Unicode.GetByteCount(message), style, timeout, out Response, true)) {
            return (MessageBoxResult)Response;
        } else {
            return MessageBoxResult.Failed;
        }
    }

    public static bool SendMessage(int sessionId, string title, string message, MessageBoxType style = MessageBoxType.BUTTON_OK, int timeout = 0)
    {
        MessageBoxResult Response = MessageBoxResult.Failed;
        return WTSSendMessage(IntPtr.Zero, sessionId, title, Encoding.Unicode.GetByteCount(title), message, Encoding.Unicode.GetByteCount(message), style, timeout, out Response, false);
    }

    [DllImport("wtsapi32.dll", EntryPoint = "WTSSendMessageW", SetLastError = true, CharSet = CharSet.Unicode)]
    static extern bool WTSSendMessage(
        // Handle to the server (null for current server)
        IntPtr Server,

        // The desktop session ID (e.g. from qwinsta output)
        // [MarshalAs(UnmanagedType.U4)]
        int SessionId,

        // The title of the message box
        string Title,

        // The length of the title string
        // [MarshalAs(UnmanagedType.U4)]
        int TitleLengthInBytes,

        // The message to display
        string Message,

        // The length of the message string
        // [MarshalAs(UnmanagedType.U4)]
        int MessageLengthInBytes,

        // The style of the message box
        // [MarshalAs(UnmanagedType.U4)]
        MessageBoxType Style,

        // The timeout in seconds
        // [MarshalAs(UnmanagedType.U4)]
        int Timeout,

        // The user's response (as an output), if bWait is set to true
        // [MarshalAs(UnmanagedType.U4)]
        out MessageBoxResult Response,

        // Whether to wait for the user's response
        bool Wait);
}
"@
}

# Import the defined C# class into PowerShell
Write-LogMessage "C# type added to PowerShell."


function Show-RemoteDesktopMessage {
    param(
        [Parameter(Mandatory)]
        [string]$Title,

        [Parameter(Mandatory)]
        [string]$Message,

        # No timeout by default
        [int]$Timeout = 0,

        # OK button by default
        [MessageBoxType]$Style = "BUTTON_OK,ICON_INFORMATION",

        # The Windows login session to send to (see `qwinsta` command)
        [int]$sessionId = ((Get-RDSession).Id ?? 1)
    )

    if (-not $sessionId) {
        Write-Error "Active Session ID not found. Cannot display message box."
        exit 1
    }

    Write-LogMessage "Calling WTSSendMessage to display message box."
    Write-LogMessage "Session: $SessionId"
    Write-LogMessage "Title: $Title"
    Write-LogMessage "Message: $Message"
    Write-LogMessage "Style: $Style"

    $result = [RemoteDesktop]::SendMessage($sessionId, $title, $message, $style)

    # Log the result
    if ($result) {
        Write-LogMessage "Message box displayed successfully in session ID $sessionId."
        Write-Output "Message box displayed successfully."
    } else {
        $errorCode = [System.Runtime.InteropServices.Marshal]::GetLastWin32Error()
        Write-LogMessage "Failed to send message box. Error code: $errorCode"
        Write-Error "Failed to send message box. Error code: $errorCode"
    }
}

function Get-RemoteDesktopResponse {
    param(
        [Parameter(Mandatory)]
        [string]$Title,

        [Parameter(Mandatory)]
        [string]$Message,

        # OK button by default
        [Parameter(Mandatory)]
        [MessageBoxType]$Style,

        # No timeout by default
        [int]$Timeout = 0,

        # The Windows login session to send to (see `qwinsta` command)
        [int]$sessionId = ((Get-RDSession).Id ?? 1)
    )

    if (-not $sessionId) {
        Write-Error "Active Session ID not found. Cannot display message box."
        exit 1
    }

    Write-LogMessage "Calling WTSSendMessage to display message box."
    Write-LogMessage "Session: $SessionId"
    Write-LogMessage "Title: $Title"
    Write-LogMessage "Message: $Message"
    Write-LogMessage "Style: $Style"

    $result = [RemoteDesktop]::QueryMessage($sessionId, $title, $message, $style)

    # Log the result
    if ($result -ne "Failed") {
        Write-LogMessage "Message box displayed successfully in session ID $sessionId and they responded with $result."
    } else {
        $errorCode = [System.Runtime.InteropServices.Marshal]::GetLastWin32Error()
        Write-LogMessage "Failed to send message box. Error code: $errorCode"
        Write-Error "Failed to send message box. Error code: $errorCode"
    }

    $result
}