This file displays a form that requests your username and password and also gives you the options to register as a new user or recover your password if you've forgotten it.

 Once you've  pressed the submit button the following code gets executed:

<?
session_start();
if(isset($_GET['reg'])){
$reg=$_GET['reg'];
}else{
$reg="";
}
if($reg==1){
$msg1="<font color="#FF0000"><b>Your details have been added,
please login</b></font>";
}elseif($reg==2){
$msg1="<font color="#FF0000"><b>You have been successfully
logged out.</b></font>";
}elseif($reg==3){
$msg1="<font color="#FF0000"><b>You have been redirected because you need to be logged on as administrator.</b></font>";
}
if(isset($_POST['submit'])){
if( empty($_POST['uname']) && (empty($_POST['upass']))){
header( "Location:Messages.php?msg=1" );
exit();
}
//transfer to shorter var
$n=$_POST['uname'];
$p=$_POST['upass'];
//connect to db
include('config.php');
$query="select * from user where uname='$n' and pw='$p'";
if($result=mysql_query($query)){
$row=mysql_fetch_assoc($result);
//check each var
if($n !=$row['uname']){
header( "Location:Messages.php?msg=2" );
exit();
}
if($p !=$row['pw']){
header( "Location:Messages.php?msg=11" );
exit();
}
if($row['isbanned']=='yes'){
header( "Location:Messages.php?msg=12" );
exit();
}
}//ifresult
//put in session vars
$_SESSION['level'] = $row['level'];
$_SESSION['status'] = 'logged';
$_SESSION['username'] = $n;
//This takes you to the admin pages; change this to take you to
wherever you want it //to go.
header("location:../admin/main.php");
exit;
}?>

Ignore the first part that falls under "if(isset($_GET['reg'])){}" since it concerns another script; we will come to it later. The next part does the following things:

• Checks to see whether a user exists. If so, the username and password is compared with the information in the database. It also checks to see whether the user is banned. If all the checks are okay, the script puts the username in a session variable and then sends the user through to the blog.
  
• If the user does not exist, the program goes to the messages page and displays an error message.

The script also checks the user's banned status. If a user is banned, then the script directs you to the Messages page. The submitted username and password is checked individually and then the appropriate action is taken. This enables the user to know exactly which of the two, username or password, is wrong.

You will also notice that some session variables are created. These are going to be used by the blog system to identify the user and by the admin script to identify whether a user indeed has admin level clearance.