Effortless E-Commerce with PHP and MySQL: User Accounts

This chapter is from the book 

The next step in the evolution of the Knowledge is Power e-commerce site is to create a system of user accounts. When the site is complete, PayPal will be the crucial part in the registration process, but just to understand the user account system on its own, as well as to be able to create an administrative user for the next chapter, let's look at user accounts as a separate entity first.

There are four primary facets to the implementation of user accounts in this chapter. First, a new user registers. Second, a registered user logs in. Third, the logged-in user logs out (in theory, many people, including me, don't always do so). Fourth, users need to be able to retrieve a forgotten password and change an existing password.

Although this example won't be storing any sensitive e-commerce data, security will still be taken seriously, for the benefit of the customers and the site itself. In a few places, I'll make recommendations as to how you can increase security even further, and the chapter ends with even more suggestions.

Defining Helper Functions

Before getting into the primary scripts, there are three helper functions that you should define. The first will greatly facilitate handling some of the site's forms. The second will transform a user-supplied password into a format that's more secure to store. And the third will redirect the browser should the user not meet the requirements for accessing a particular page.

There are a few benefits to using these custom functions:

• Keeps complex logic from cluttering up other code
• Allows the same logic to be used in multiple scripts
• Makes changes to the logic a snap

The last two are really the key points: If you separate out processes, they can be used by different parts of a site without having to repeat the code. And if you later decide you need to tweak the process, you can do so in one place.

Creating Form Inputs

The functionality provided by the scripts in this chapter is almost entirely form-based: The user must complete a registration, login, change password, or forgot password form. All these forms use just two types of form inputs—text and password (not counting the submit buttons). An input starts off with this simple HTML:

   <input type="type" name="name" id="name" />

For example:

   <input type="text" name="username" id="username" />

In cases where the form was submitted but not properly completed, the user will be presented with the form again. As a convenience, the form should remember the entered values (that is, it should be sticky). To achieve that effect, you need to add value="whatever value" to each input. In PHP code, that would be:

<input type="text" name="username" id="username" 
 value="<?php echo $_POST['username']; ?>"/>

However, the first time the form is loaded, $_POST['username'] won't be set, so the code should really be:

<input type="text" name="username" id="username" value=
 "<?php if (isset($_POST['username'])) echo $_POST['username']; ?>" />

If the user, for whatever reason, used quotation marks in their value, the quotation marks will mess up the HTML. Figure 4.1 shows the result if the user enters Jeff "The Dude" Lebowski as the username. To protect against that, you can use the htmlspecialchars() function (Figures 4.2 and 4.3):

\<input type="text" name="username" id="username" value=
 "<?php if (isset($_POST['username'])) echo htmlspecialchars(
 $_POST['username']); ?>" />

And, if Magic Quotes is enabled, the stripslashes() function should be applied to the value. You'll add that code shortly, but first, there's one more complication: If the form isn't completed properly, it'd be nice to add a CSS class to the input so that it's displayed with a red border:

<input type="text" name="username" id="username" value="
 <?php if (isset($_POST['username'])) echo htmlspecialchars(
 $_POST['username']); ?>" <?php if (/* error on this input */)
 echo ' class="error"'; ?> />

Also, in that case, the error message should be added after the input (Figure 4.4):

<input type="text" name="username" id="username" value="
 <?php if (isset($_POST['username'])) echo htmlspecialchars(
 $_POST['username']); ?>" <?php if (/* error on this input */)
 echo ' class="error"'; ?> /> <?php if (/* error on this input */)
 echo '<span class="error">' . /* error message */ . '</span>'; ?>

As you can tell, there's a lot of logic going into these inputs and their error handling, and they haven't even addressed Magic Quotes yet. The code above is just a mess to look at; it'll need to be used a dozen times; and if you later decide to handle things differently, you'll be editing code all day. So instead, let's write one function that does all this automatically. In Chapter 5, "Managing Site Content," forms will also contain textareas, so this function will be flexible enough to handle those, too.

1. Create a new PHP file in your text editor or IDE to be named form_functions.inc.php.

   This file should be stored in the includes directory.

   NOTE

   I'm using the plural functions in the file name even though only one function is being defined. Other functions might be added to it later (in theory).

2. Begin defining the function:

   <?php
   function create_form_input($name, $type, $errors) {
   

   The function takes three arguments. The first is the name that will be given to the element. The second is the element type, which will be either text or password in this chapter, and textarea in the next. The third argument will be an array of errors.

3. Check for and process the value:

   $value = false;
   if (isset($_POST[$name])) $value = $_POST[$name];
   if ($value && get_magic_quotes_gpc()) $value = stripslashes($value);
   

   First, the function assumes that no value exists. Then, if a value does exist for this input in $_POST, that value is assigned to $value. The third step strips extraneous slashes from the value, but only if Magic Quotes is enabled.

   NOTE

   If you're new to programming, I recommend writing conditionals over multiple lines and always using curly brackets, but this book will have some single-line conditionals to save space.

   This function assumes that the form uses the POST action. You could create another argument that accepts POST or GET and checks the corresponding superglobal for the value, if you want to make the function even more flexible.

4. Check the input type:

   if ( ($type == 'text') || ($type == 'password') ) {
   

   This function will create text inputs, password inputs, and textareas. The first two are virtually the same in syntax, except for the type value used in the HTML. The function starts by handling those two types.

5. Begin creating the input:

   echo '<input type="'.$type.'"name="'.$name.'" id="'.$name.'"';
   

   This is the initial shell of the HTML input, with its type, name, and id properties.

6. Add the input's value, if applicable:

   if ($value) echo ' value="' . htmlspecialchars($value) . '"';
   

   If the $value variable has a value, then it should be added to the input, after running it through htmlspecialchars().

7. Check for an error:

   if (array_key_exists($name, $errors)) {
       echo 'class="error" /> <span class="error">' . $errors[$name] .
       '</span>';
   } else {
       echo ' />';
   }
   

   The $errors variable will be assigned to an array when the function is called. That array will contain every form error that occurred, indexed by the input's name (you'll see this in the scripts that handle the forms). So if the array has a key with the same name as this input, the error class is added to the input and then the error message is added after the input (see Figure 4.4).

   If no such array element exists, then the input is completed without any additional class styling.

8. Check if the input type is a textarea:

   } elseif ($type == 'textarea') {
   
         

9. Display the error first:

   if (array_key_exists($name, $errors)) echo ' <span class="error">' .
    $errors[$name] . '</span>';
   

   Unlike with the text and password inputs, where the error message will be displayed to the right of the input itself, for textareas, I want to display the error message above the textarea, so that it's most obvious (Figure 4.5).

   

   Figure 4.5

10. Start creating the textarea:

    echo '<textarea name="' . $name . '" id="' . $name . '" rows="5" cols="75"';
    

    Here, the textarea's opening tag is created, providing dynamic name and id values. I've chosen to hardcode the textarea's size into this function to make the default scale a bit bigger than what the browser would otherwise create.

11. Add the error class, if applicable:

    if (array_key_exists($name, $errors)) {
       echo ' class="error">';
    } else {
        echo '>';
    }
    

    The error class must be added to the opening textarea tag, if an error exists with this element.

12. Add the value to the textarea:

    if ($value) echo $value;
    

    The value for textareas is written between opening and closing textarea tags. Step 11 closed the opening tag and Step 13 will create the closing one, so the value should just be printed here.

13. Complete the textarea:

    echo '</textarea>';
    

14. Complete the function:

       
       } // End of primary IF-ELSE.
    } // End of the create_form_input() function.
    
          

15. Save the file.

    Again, I'm not using a closing PHP tag, the reason for which I discussed in Chapter 3, "First Site: Structure and Design."

Protecting Passwords

The next helper function will turn the user-supplied password into a more secure format to be stored in the database. Passwords can be represented in three ways:

• In plain text, which is a terrible thing to do
• In an encrypted format, which can be decrypted
• In a hashed format, which cannot be decrypted

If you store passwords in an encrypted format, it's safe from prying eyes and can be retrieved when necessary. But if someone gets onto your server and can find your code for performing the decryption, they'll be able to view every user's password. And it turns out that you don't really need passwords to be decryptable: It doesn't matter whether anyone can ever see the plain text in its original form again or not.

An alternative is to create a hash of the password, a hash being a representation of data. For example, MD5 is a hashing algorithm that's been around for years. The MD5 hash of the word password is 5f4dcc3b5aa765d61d8327deb882cf99; the MD5 hash of the word omnivore is 04f7696e917f292f99925f80fcdb1db1. You can create a hash out of any piece of data, and, in theory, no two pieces of data have the same hash.

Storing the hash version of a password is more secure in that it cannot be decrypted. If a hacker gets your data, the best she or he can do is create hashes of common words in the hope that she or he finds the matching hash (this is called a "dictionary attack"). But storing a hash still makes logging in possible: When a user logs in, the hashed version of their login password just needs to equal the already stored hashed version. If the two hashes equate, the submitted password is correct.

Once you've decided to hash the passwords, you'll need to choose what hashing algorithm (or, formula) to use and where the hashing should take place. By the latter I mean that you can hash the password in either the database or in your PHP code. Normally, I recommend having the database do as much as possible, but PHP has more sophisticated hashing functions available than MySQL, and if you perform the hash in PHP, you no longer have the risk of sending a plain text password to the database.

MD5 is a common, legacy, hashing algorithm, but not very secure. An improvement is SHA or SHA1, which is fine for many applications. For improved security, I'm going to turn to PHP's relatively new hash_hmac() function. This function is part of PHP's Hash extension, enabled by default as of PHP 5.1.2.

Hashing algorithms create hexadecimal representations: fixed strings containing only numbers and letters (as in the password and omnivore examples). You can store a hash in a database in that format. But as an improvement, it's more efficient to store binary data in the database instead of character data, so let's tell the hashing function to return binary data. Since binary data can contain characters that will break queries (such as a single quotation mark or a back-slash), the output should still be run through the mysqli_real_escape_string() function. The resulting password generating function is defined like so:

function get_password_hash($password) {
   global $dbc;
   return mysqli_real_escape_string ($dbc, hash_hmac('sha256',
    $password, 'c#haRl891', true));
}

The hash_hmac() function takes up to four arguments. The first is the algorithm to use, SHA256 in this case. This is an improved version of SHA1.

The second argument is the data to be hashed. This will be the value assigned to $password when the get_password_hash() function is called.

The third argument is a hash key, which makes the generated hash unique. The same key must be used when comparing two hashes.

The fourth argument is optional. If you use true , the output will be in raw, binary format. Otherwise, the output will be hexadecimal characters.

The output of the hash_hmac() function is then run through mysqli_real_escape_string() before being returned.

If your server doesn't support hash_hmac(), you could use this syntax instead:

return mysqli_real_escape_string ($dbc, sha1($password, true));

Just using sha1(), instead of the SHA256 algorithm, isn't as secure, but SHA256 level of security may not be warranted in your situation.

Because this function will be used with database queries, and because it requires the database connection, it should be defined in the mysql.inc.php script.

Redirecting the Browser

The third helper function will be used to limit access to pages to proper users. For example, a couple of public pages should only be viewable by current users, and the two administrative pages should be viewable by administrators only. If the current user doesn't meet the page's criteria, the browser should be redirected elsewhere, and the current page should be terminated (Figure 4.6). By writing this process in a function, any page that requires authorization will need to invoke only this function, without any additional logic.

Since the configuration file, config.inc.php , will be included by every script in the site, it makes sense to define this function there:

function redirect_invalid_user($check = 'user_id', $destination =
 'index.php', $protocol = 'http://') {
   if (!isset($_SESSION[$check])) {
       $url = $protocol . BASE_URL . $destination;
       header("Location: $url");
       exit();
   }
}

The function takes three arguments, all of which are optional. The first is the session array element to validate against, the default being user_id. In other words, if $_SESSION['user_id'] is not set, the user hasn't logged in and shouldn't be looking at this page. In Chapter 5, this same function will be used to restrict access to administrators or to users whose accounts have not expired.

The second argument to the function is the page to which the user should be redirected. By default, this will be the home page, but you could send them to the registration page or anywhere by changing the value passed to this function.

The third argument is the protocol to use, with the default being http://. I've included this option so that users can be redirected to SSL or non-SSL pages.

Within the function, a conditional checks the session variable. If it's not set, a redirection URL is defined by concatenating the protocol and destination to the BASE_URL constant (also defined in the configuration file). Then a header() call performs the actual redirection. Finally, the exit() function (language construct, technically) will terminate the script (the one that called this function). This is necessary because PHP will continue to execute a script after a header() call, even if the browser has already moved on.

When creating the login script later in this chapter, you'll have to keep in mind how this redirection function works. Specifically, authorization is based upon a value being set, not based upon what that value is. For example, a logged-in user just has any user_id value and an administrator will also have any user_admin value. But non-administrators should not be assigned a user_admin value, even if that value is false or no.

I imagine this function only being called immediately after including the configuration file (see Figure 4.6), so the function does not check that headers haven't already been sent, which would prevent the browser from being redirected. If you want to account for that possibility, just use the headers_sent() function in a conditional. If it returns false, redirect the user; if it returns true, include the header and footer and display an error message:

if (!headers_sent()) {
    // Redirect code.
} else {
    include_once('./includes/header.html');
    trigger_error('You do not have permission to access this page. Please
     log in and try again.');
    include_once('./includes/footer.html');
}