Home > Articles > Programming > PHP

This chapter is from the book

This chapter is from the book

Authenticating Users Against Text Files

Not all sites contain a database back-end to store data, and some sites probably will never require them. Still, you may want to limit access to certain parts of the site or even the entire site. One way to do this is to authenticate against a text file stored someplace on the server, preferably out of the Web server directory so that there is no way it can be accessed by someone with a Web browser.

This method only requires the standard file functions, as well as the MD5 encryption function.

This script serves a dual purpose. It allows you to add users to a password file, as well as test authentication. This way, you can create a blank text file and easily fill it with some username/password combinations so that you can test the functionality of the script.

This script is not meant to be used in its entirety to check passwords on a site. You would need to remove the functions that allow you to add users before you placed the script in your own site.

Script 7-2 file_authentication.php

 1.  <?
 2.  $password_file = "C:/apache/passwords/pass.txt";
 4.  function check_pass($login, $password) {
 5.    global $password_file;
 6.    if(!$fh = fopen($password_file, "r")) {die("<P>Could Not Open Password File");}
 7.    $match = 0;
 8.    $password = md5($password);
 9.    while(!feof($fh)) {
10.      $line = fgets($fh, 4096);
11.      $user_pass = explode(":", $line);
12.      if($user_pass[0] == $login) {
13.        if(rtrim($user_pass[1]) == $password) {
14.          $match = 1;
15.          break;
16.        }
17.      }
18.    }
19.    if($match) {
20.      return 1;
21.    } else {
22.      return 0;
23.    }
24.    fclose($fh);
25.  }
27.  function print_login_form($login) {
28.    ?>
29.    <p>Please Log In:
30.    <form action=file_authentication.php method=post>
31.    <p>Login: <input type="text" name="login" value="<?=$login?>">
32.    <br>Password: <input type="password" name="password">
33.    <br><input type="submit" name="checkpass" value="Login!">
34.    </form>
35.    <?
36.  }
38.  function print_add_form() {
39.    ?>
40.    <p>Add New User:
41.    <form action=file_authentication.php method=post>
42.    <p>Login: <input type="text" name="adduser">
43.    <br>Password: <input type="password" name="addpass">
44.    <br><input type="submit" name="add" value="Add User!">
45.    </form>
46.    <?
47.  }
49.  function add_user($adduser, $addpass) {
50.    global $password_file;
51.    if(!$fh = fopen($password_file, "a+")) { die("<P>Could Not Open Password File"); }
52.    rewind($fh);
53.    while(!feof($fh)) {
54.      $line = fgets($fh, 4096);
55.      $user_pass = explode(":", $line);
56.      if($user_pass[0] == $adduser) {
57.        echo "<h2>Duplicate Login. Invalid!</h2>";
58.        return 0;
59.      }
60.    }
61.    $add = $adduser . ":" . md5($addpass) . "\n";
62.    if(!fwrite($fh, $add)) { die("<P>Could Not Write To Password File"); }
63.    fclose($fh);
64.    echo"<h2>User Added!</h2>";
65.  }
66.  /***** MAIN *****/
67.  if(isset($checkpass)) {
68.      if(check_pass($login, $password)) {
69.        echo "<h2>Login Success!</h2>";
70.      } else {
71.        echo "<h2>Login Failed</h2><p>Bad username or password. Login and Password are 
case-sensitive. Try again:";
72.      print_login_form($login);
73.      }
74.  } elseif(isset($add_form)) {
75.    print_add_form();
76.  } elseif(isset($add)) {
77.    add_user($adduser, $addpass);
78.  } else {
79.    print_login_form("");
80.  }
81.  ?>
82.  <p>You can <a href=file_authentication.php?add_form=1>Add Users</a> or <a 
href=file_authentication.php>login</a> an existing user.

Script 7-2. file_authentication.php Line-by-Line Explanation




Define the file that contains the passwords. Note that you should specify the correct path on your machine that points to the password file. On *nix-based systems, you'd obviously omit the "C:\" nonsense in the path.


Create a function that checks the user-entered password against the username/password combination stored in the password file.


Allow the password file to be read and modified globally by this function.


Attempt to open the file and assign it to a file pointer. If the file cannot be opened, then print an error and exit from the script.


Initialize a variable to track a username/password match. Initialize it to false (0) to assume the password is incorrect.


Since the passwords are stored encrypted, encrypt the user-entered password using the MD5 function.


Create a while loop that searches through the file until the end of file (EOF) is reached.


For each iteration of the loop, get one line from the file and place it in the $line variable.


Create an array of the line obtained from the file using the explode function. Since the usernames and passwords are stored in the format:


and the explode() function breaks up the line on every ":", the script places two items into the $user_pass array: the username at index [0] and the password at index [1].


Check if the username from the file, which is stored in $user_pass[0], matches the username entered by the user, $login.


If the user-entered username matches the username obtained from the file, then check to see if the password from the file, $user_pass[1], matches the password entered by the user, $password.


If the passwords match, then set the $match variable to true (1), since the user-entered username and password match the ones contained in the password file.


If the passwords match, then break from the loop.


Close out the password-checking if statement.


Close out the username-checking if statement.


Close out the while loop.


If there was a match, then return true to the calling program or function.


If there was no match, then return false to the calling program or function.


Close the file.


End the function declaration.


Create a function that prints a login form to the screen. The function takes one argument, called $login, which is used to automatically re-enter the username if there was no match from a previous attempt at logging in.


Stop parsing the page as PHP.


Begin displaying the login form.


Print the username field. If this is a subsequent attempt to log in, then automatically enter the username.


Continue printing the form to the page.


Start parsing the page as PHP again.


End the function declaration.


Create a function that prints a form allowing you to add username/password combinations to the password file.


Stop parsing the page as PHP and print out a standard HTML form, then continue parsing the page as PHP.


End the function declaration.


Create a function that adds a username and password combination to the password file. The function takes two arguments: $adduser and $addpass.


Allow the password file to be read and modified globally by this function.


Attempt to open the file and assign it to a file pointer. If the file cannot be opened, then print an error and exit from the script.


Since we opened the file using append mode ("a+") on line 51, rewind the file so that the file pointer is at the beginning of the file. The append mode places the file pointer at the end of the file by default.


Create a while loop that searches through the file until the end of file (EOF) is reached.


For each iteration of the loop, get one line from the file and place it in the $line variable.


Create an array of the line obtained from the file using the explode function.


Check to see if the username stored in $user_pass[0] is the same as the username entered into the Add User form. Usernames should always be unique! This line checks to make sure that a duplicate username is not being entered into the password file.


If the usernames match, then you are trying to enter a duplicate username. Print out a message to the users informing them that the username they entered is invalid.


Return false to the calling program or function.


Since this line has been reached, it means that the username entered was unique (if it was not, then the function would have terminated with the return on line 58). Create a username/password combination by prepending the username to the MD5 encrypted form of the password. A colon is placed in between the two so that the script can parse easily when it checks usernames and passwords. Colons do not occur as output in MD5 encryption, so they are safe characters to use to delimit the two values. (Note that the script doesn't forbid colons in the usernames, which would cause user authentication to always fail if a user placed a colon in a username.)


Attempt to write the new username/password combination to the end of the file. You know you are at the end of the file, since the while loop just parsed the entire file. If the write attempt fails, then display an error and kill the script.


Close the file.


Print a message letting the user know the password was added to the password file.


End the function declaration.


Begin the main file execution.


Check to see if the $checkpass variable has been set. If it is set, this means that the login form was submitted to the script.


If the $checkpass variable is set, run the check_pass() function using the user-entered username and password.


If the check_pass() function returns true (1), notify the user that authentication succeeded. At this point, you would normally display the content that you were protecting with the user authentication.


If the check_pass() function returned false, then print a message informing the user of the error.


If the $checkpass variable is not set, but the $add_form variable is set, then print out the form to allow you to add new username/password combinations to the password file.


If the $checkpass variable is not set and the $add_form variable is not set, but the $add variable is set, then run the add_user function using the values entered into the Add User form.


If none of the above is true, then print the login form using a null value as the argument so that the login_form function does not generate a warning about use of an uninitialized variable.


Stop parsing the page as PHP.


Print a line to the browser that provides two links. The first is a link that sets the add_form variable so that the add_form function is called and you can add username/password combinations to the password file. The second link is used to display the login form after you have added a user.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020