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Saturday, May 10, 2008

Implementing User Authorization Using Session Control

Implementing User Authorization Using Session Control

You may want to read An Example of User Authentication System in PHP, What is Session Control/Variables? before reading this post.

In this post we are going to create a ‘secret’ site whose pages will only be accessible after logging in using the correct username and password. We will be using our knowledge of Session Control/Variables since we want authorization for the whole site and not a single page.

The site that we are going to create will have three ‘secret’ pages plus one-one page for logging in and homepage.

Let’s start by having a look at the login page code:

<html>
<head>
<title>My Web Site | Login</title>
</head>

<body>
<h1>My Web Site</h1>
<h2>Login </h2>
<?php
define
('USERNAME','happyjoe');
define('PASSWORD','123456');

//if submit button was pressed
//that means form was submitted
if(isset($_POST['submit']))
{
    
//fetch other form data
    
$username=$_POST['username'];
    
$password=$_POST['password'];
    
    
//start a session
    
session_start();

    
//match username & password
    
if($username==USERNAME && $password==PASSWORD)
    {
        
//save session variable with the username
        //which will be unique
        
$_SESSION['user']=$username;
        
//redirect to homepage
        
header("Location: home.php");
    }
    else
        echo 
"<p style=\"color:#ff0000;\">Incorrect 
    Username/Password. Please Try Again.</p>"
;
}
else
//requesting the login page
{
    
//if requesting the login page
    //check if already logged in
    //and redirect to homepage if true

    //start session
    
session_start();
    if(isset(
$_SESSION['user']))
    {
        
//redirect to homepage
        //if already logged in
        
header("Location: home.php");
    }
}
//if not logged in show the login page
?>
<form name="form1" id="form1" method="post" action="">
  <table width="30%" border="0" cellspacing="0" cellpadding="0">
    <tr> 
      <td>Username</td>
      <td><input name="username" type="text" id="username" /></td>
    </tr>
    <tr> 
      <td>Password</td>
      <td><input name="password" type="password" id="password" /></td>
    </tr>
    <tr>
      <td>&nbsp;</td>
      <td><input name="submit" type="submit" id="submit" 
    value="Submit" /></td>
    </tr>
  </table>
</form>
</body>
</html>

Now the homepage:

<html>
<head>
<title>My Web Site | Login</title>
</head>

<body>
<h1>My Web Site</h1>
<?php
//start session again
session_start();
//if someone is requesting this page
//without logging in
if(!isset($_SESSION['user']))
{
    echo 
"<p>You are not Authorized to view this page. Please <a href=\"login.php\">Login</a> first.</p>";
    
//exit script; don't execute any further
    
exit;
}
//if logged in
?>
<h2>Secret Pages </h2>
<ul>
  <li><a href="page1.php">Page1</a></li>
  <li><a href="page2.php">Page2</a></li>
  <li><a href="page3.php">Page3</a></li>
</ul>
<?php
//show user name at the bottom
echo "<p>USER: <i>".$_SESSION['user']."</i></p>";

?>
</body>
</html>

You can see that the content of the homepage will only be accessible when the session variable has been set by successful login from the login page.

The homepage after login will look something like below:

Home Pag after loggin in

As you can see there are three links to the bottom. The codes for these pages are listed below:

For page one:

<html>
<head>
<title>My Web Site | Page1</title>
</head>

<body>
<h1>My Web Site</h1>
<?php
//if someone is requesting this page
//without logging in
session_start();
if(!isset(
$_SESSION['user']))
{
    echo 
"<p>You are not Authorized to view this page. 

Please <a href=\"login.php\">Login</a> first.</p>";
    
//exit script; don't execute any further
    
exit;
}
//if logged in
?>
<h2>Page1</h2>
<p>this is a secret page.</p>
</body>
</html>

For page two:

<html>
<head>
<title>My Web Site | Page2</title>
</head>

<body>
<h1>My Web Site</h1>
<?php
//if someone is requesting this page
//without logging in
session_start();
if(!isset(
$_SESSION['user']))
{
    echo 
"<p>You are not Authorized to view this page. 

Please <a href=\"login.php\">Login</a> first.</p>";
    
//exit script; don't execute any further
    
exit;
}
//if logged in
?>
<h2>Page2</h2>
<p>this is a secret page.</p>
</body>
</html>

For page three:

<html>
<head>
<title>My Web Site | Page3</title>
</head>

<body>
<h1>My Web Site</h1>
<?php
//if someone is requesting this page
//without logging in
session_start();
if(!isset(
$_SESSION['user']))
{
    echo 
"<p>You are not Authorized to view this page. 

Please <a href=\"login.php\">Login</a> first.</p>";
    
//exit script; don't execute any further
    
exit;
}
//if logged in
?>
<h2>Page3</h2>
<p>this is a secret page.</p>
</body>
</html>

If you look closely, each ‘secret’ page checks to see if the session variable is set or not (which can only be after successful login). So, even direct access to these pages is restricted.

In case someone tries to access these pages directly without logging in, he/she would see:

It'd look like this when anyone tries to access this page without loggin in


We could have created the whole site using the method outlined in the post How does CMS Create Dynamic Pages to create the whole site off just one script but I wanted to illustrate the fact that session variables are accessible from different pages too, across a session.

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