Check for certificate expiration

Certificate.ps1

function Get-CertificateExpiration {

  <#
  .SYNOPSIS
  Displays a list of certificates that will expire soon.
  #>

  param(
    $Threshold = 30, #Number of days to look for expiring certificates
    [string[]]$ComputerName
  )

  $Deadline = (Get-Date).AddDays($Threshold)
  
  if ($ComputerName) { 
    $cert = Invoke-Command -ComputerName $ComputerName { Get-ChildItem Cert:\ -Recurse }
  } else { 
    $cert = Get-ChildItem Cert:\ -Recurse
  }
  $cert | Foreach-Object {
    If ($_.NotAfter -le $Deadline) { 
      $_ | Select-Object *, @{Name="Expires In (Days)"; Expression={($_.NotAfter - (Get-Date)).Days}}
      # other interesting properties: Issuer, Subject, NotAfter
    }
  }
}