Code:
$BSPHostName = "172.16.50.1"
$objHTTP = CreateObject("MSXML2.ServerXMLHTTP")
$objHTTP.SetOption(2, 13056)
$objHTTP.Open("POST", "https://"+$BSPHostName+"/portal/logout", NOT 1)
$objHTTP.SetRequestHeader("Content-Type", "application/x-www-form-urlencoded")
$objHTTP.Send("purl=&submit=Logout")
$objHTTP = ""