Check if user has Administrator role

administrator_context.ps1

function Test-AdministratorContext {
    [CmdletBinding()]param()
    $CurrentWindowsIdentity = [System.Security.Principal.WindowsIdentity]::GetCurrent()
    $CurrentWindowsPrincipal = New-Object System.Security.Principal.WindowsPrincipal($CurrentWindowsIdentity)
    $IsAdministratorContext = $CurrentWindowsPrincipal.IsInRole([System.Security.Principal.WindowsBuiltInRole]::Administrator)
    Write-Verbose "Current Context Is Administrator = $IsAdministratorContext"
    return $IsAdministratorContext
}

administrator_warning_message.ps1

#Check for Admin rights
if (-not ([Security.Principal.WindowsPrincipal] [Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole] "Administrator")) {
    Write-Warning "$($MyInvocation.MyCommand) cannot be run because the current Windows PowerShell session is not running as an administrator. Start Windows PowerShell as an administrator and then try running the function again."
    exit
}

check_admin_role.ps1

# Adminsitrator role check
function IsLocalAdministrator() {
	$CurrentWindowsIdentity = [System.Security.Principal.WindowsIdentity]::GetCurrent()
	$CurrentWindowsPrincipal = New-Object System.Security.Principal.WindowsPrincipal($CurrentWindowsIdentity)
	$IsInWindowsBuiltInAdministratorRole = $CurrentWindowsPrincipal.IsInRole([System.Security.Principal.WindowsBuiltInRole]::Administrator)
	return $IsInWindowsBuiltInAdministratorRole
}

# One-liner
(New-Object System.Security.Principal.WindowsPrincipal([System.Security.Principal.WindowsIdentity]::GetCurrent())).IsInRole([System.Security.Principal.WindowsBuiltInRole]::Administrator)

system_context.ps1

function Test-SystemContext {
    [CmdletBinding()]param()
    $CurrentWindowsIdentity = [System.Security.Principal.WindowsIdentity]::GetCurrent()
    $IsSystemContext = $CurrentWindowsIdentity.User.Value -eq 'S-1-5-18'
    Write-Verbose "Current Context Is SYSTEM = $IsSystemContext"
    return $IsSystemContext
}