$_SESSION["username"] = "$username";
$_SESSION["user_id"] = "$user_id";
$_SESSION["act_type"] = "$act_type";

<?php

session_start();

$user = 'jane';
$pass  = '654321';

if ( $user == $_POST[user] AND $pass == $_POST[pass] ) {

    $_SESSION[user] = $user;
    header("location: secure.php");
}
else {
    echo "Bad Login";
}

?>

<form name="form1" method="post" action="index.php">

    Username: <input name="user" type="text">
    <br />
    Password: <input name="pass" type="password">
    <br /><br />
    <input type="submit" name="Submit" value="Login">
</form>

<?php

session_start();

if ( !isset($_SESSION[user]) ) {

    header("location: index.php");
}

?>
Secure Page

<?php

session_start();

$user = 'joe';
$pass  = '123456';

if ( $user == $_POST[user] AND $pass == $_POST[pass] ) {

    $_SESSION[user] = $user;
    header("location: secure.php");
}
else {
    echo "Bad Login";
}

?>

<form name="form1" method="post" action="index.php">

    Username: <input name="user" type="text">
    <br />
    Password: <input name="pass" type="password">
    <br /><br />
    <input type="submit" name="Submit" value="Login">
</form>

<?php

session_start();

if ( !isset($_SESSION[user]) ) {

    header("location: index.php");
}

?>
Secure Page

$_SESSION["s1_username"] = $username;
$_SESSION["s1_user_id"] = $user_id;
$_SESSION["s1_act_type"] = $act_type;

$_SESSION["s2_username"] = $username;
$_SESSION["s2_user_id"] = $user_id;
$_SESSION["s2_act_type"] = $act_type;

foreach($_SESSION as $key => $value)
{
  if (strpos($key, 's1_') === 0)
  {
   unset($_SESSION[$key]);
  }
}

foreach($_SESSION as $key => $value)
{
  if (strpos($key, 's2_') === 0)
  {
   unset($_SESSION[$key]);
  }
}