Powershell: Add a platform agnostic way to detect when running elevated

[bradwilson]

When writing a PowerShell script, it would be nice to know if you're running in an elevated context (UAC in Windows, as root on *nix). You can do platform-specific things today, but it should be easily available without regard to platform.

[SteveL-MSFT]

CoreFx has an open issue to add API support: https://github.com/dotnet/corefx/issues/27304

Depending on how that goes (whether it's Unix specific, for example), perhaps we should consider a $IsAdmin automatic variable.

[iSazonov]

We have Test-IsElevated in out HelpersCommon.psm1. We could re-implement it on C#. Although the use of whoami/id is under question.

[ThomasNieto]

Looks like the CoreFx issue was closed and the recommended solution was to:

https://github.com/dotnet/runtime/issues/25118#issuecomment-367407469

To check if you are running as root on Unix:

1. add a PackageReference to Mono.Posix.NETStandard
2. Change IsAdminstrator to the following:

        public static bool IsAdministrator =>
            RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ?
                new WindowsPrincipal(WindowsIdentity.GetCurrent())
                    .IsInRole(WindowsBuiltInRole.Administrator) :
                Mono.Unix.Native.Syscall.geteuid() == 0; 

[bradwilson]

This is what I landed on:

$isDesktop = ($PSVersionTable.PSEdition -eq "Desktop")

if ($isDesktop -or $IsWindows) {
    $windowsIdentity = [System.Security.Principal.WindowsIdentity]::GetCurrent()
    $windowsPrincipal = new-object 'System.Security.Principal.WindowsPrincipal' $windowsIdentity
    $isAdmin = $windowsPrincipal.IsInRole("Administrators") -eq 1
}
else {
    $isAdmin = ((& id -u) -eq 0)
}

Doesn't make sense to add a reference to Mono.Postix.NETStandard from PowerShell.

[iSazonov]

It is better to have in .Net.

.Net team asks to open new issue with API proposal. If you want to get any progress I suggest to open such issue there while they plans .Net 6.0.

[bradwilson]

@iSazonov This doesn't need to be a .NET feature. It could absolutely be a PowerShell feature.

[iSazonov]

We prefer to follow .Net in the repository.

The API is problematic because it depends on platforms. It should take into account all Unix clones and specific "platforms" like WebAssembly/Blazor. This requires complex testing and discussion.