Sock It To Me, Baby! - PHP

Want to restrict access to certain sections of your Web site?Or customize page content on the basis of user preferences? Or eventrack user movement across your site? Well, the bad news is that you'llneed to learn how to authenticate users on your site. The good news isthat this tutorial has everything you need to get started.

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By: The Disenchanted Developer, (c) Melonfire

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March 13, 2002

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So that takes care of authentication via flat file and database. There is one more authentication option, though it's not one that's very common in the Web environment. In the arena of networked set-top applications, there often exist proprietary authentication schemes, and proprietary methods of performing user authentication.

In one such system that I worked on, authentication took place via a socket server listening on a specific port for connections. This socket server could accept a username/password combination, in the form "username:password" and return an appropriate result code depending on whether or not the validation was successful.

In such a system, the authenticate() function in the "login.php" script could be further modified to use a socket connection to perform the validation, rather than a database or a file. Take a look at what this might look like:

<?
// login.php - performs validation 
$status = authenticate($f_user, $f_pass);
// if  user/pass combination is correct
if ($status == 1)
{
// initiate a session
session_start();
// register some session variables
session_register("SESSION");
// including the username
session_register("SESSION_UNAME");
$SESSION_UNAME = $f_user;
// redirect to protected page
header("Location: /inner.sanctum.php");
exit();
}
else
// user/pass check failed
{
// redirect to error page
header("Location: /error.php?e=$auth");
exit();
}
// authenticate username/password against data from a socket connection
// returns: -1 if user does not exist
//           0 if user exists but password is incorrect
//           1 if username and password are correct
function authenticate($user, $pass)
{
// where is the socket server?
$host ="192.168.1.99";
$port = 1234;
// assign authentication status -1
$result = -1;
// open a client connection
$fp = fsockopen ($host, $port, $errno, $errstr);
if (!$fp)
{
return $result;
}
else
{
// get the welcome message
fgets ($fp, 1024);
// create the input string
$message = "$user:$pass";
// write the user string to the socket
fputs ($fp, $message);
// get the result
// this will be 0 or 1
$result .= fgets ($fp, 1024);
// close the connection
fputs ($fp, "END");
fclose ($fp);
// trim the result
$result = trim($result);
}
return $result;
}
?>

Fairly simple, this. A socket connection is opened to the socket server from the PHP script (which acts as a client), and the form data transmitted to it via a call to fsockopen(). The socket server then internally runs a proprietary validation routine to test whether or not the data passed to it is correct, and returns a result code to the client. This return value can be intercepted via the fgets() function, and returned to the main program, which then again makes the decision of what to do next.

As I said, it's unlikely that you'll ever find yourself using this. It's included here for illustrative purposes only, as an example of yet another way of performing authentication in a proprietary environment.{mospagebreak title=Entering The Inner Sanctum} So that takes care of the initial verification. Assuming the user has been successfully validated, all three versions of the "login.php" script above would create a new session and redirect the user to the protected page "inner.sanctum.php".

Now for the second part of the validation, and the one that you might not have thought of. Every protected page must itself include program code to ensure that only authorized users have access to it. Without this code, it would be possible for anyone to access the page directly, just by typing the URL into their browser's address bar.

Here's what the code for inner.sanctum.php looks like:

<?
// inner.sanctum.php - secure page
// session check
session_start();
if (!session_is_registered("SESSION"))
{
// if session check fails, invoke error handler
header("Location: /error.php?e=2");
exit();
}
?>
<html>
<head>
<basefont face="Verdana">
</head>
<body>
<center>
Welcome to the inner sanctum. We've been waiting for you. </center> <p
align="right"> <font size="-1"><a href="logout.php">Goodbye</a></font>
</body>
</html>

Note the code right at the top of the page. I'm first checking to ensure that a valid session exists for this user, and only proceeding to display the page if it does. If a valid session does not exist, it would imply that the user was either unable to log in successfully, or that (s)he bypassed the login screens altogether and attempted to access the page directly. In either case, access should be denied - which is why I've used the header() function to redirect the user to the error page immediately.

This is a very primitive check, of course - I'm merely testing to see whether a session exists. In the real world, you'd typically want to add a few more checks, such as verifying the user's permission level or role (common in the case of multi-tiered, group-based systems).

In order to understand the difference, try accessing the page above by directly typing the URL into your browser's address bar without logging in first. You should not be allowed access. Then comment out the PHP code at the top of the script, and try again. You'll see that, this time, you can access this "protected" page without needing to log in first.

Here's what the page looks like:

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