public static function verifySession()
 {
     if (isset($_SESSION["username"]) && isset($_SESSION["token"])) {
         // they are logged in
         $agent = apache_request_headers()["User-Agent"];
         $encrypted = sha1($_SESSION["username"] . $agent);
         //echo $agent . "<br />";
         //echo "[sha!]" . sha1($agent) . "[!sha]";
         if ($encrypted == $_SESSION["token"]) {
             // echo "valid";
             // echo "<br />Token: ".$_SESSION["token"];
             //echo "<br />Challenge: ".$encrypted;
             //echo "<br />Username: "******"username"];
             //verified
         } else {
             AuthenticationManager::destroySession();
             //echo "failed <br />".$encrypted."<br />";
         }
     } else {
         //echo "not logged in";
         //not logged in
     }
 }