Google Apps Script: Web App Login Guide

by Alex Braham 40 views

Let's dive into creating a secure and functional login system for your Google Apps Script web applications. Securing your web apps is super important, guys. You don't want just anyone messing with your stuff, right? This guide will walk you through the essential steps and considerations to implement a robust login mechanism. I will show you how to write code to accomplish the goal. So, buckle up, and let's get started!

Setting the Stage: Why a Login System?

Before we jump into the code, let's quickly cover why you'd even need a login system in the first place. Think about it: If you're building a web app with Google Apps Script, chances are you're dealing with some sensitive data or functionality. Maybe you're managing a database of customer information, or perhaps you've created a tool that automates important tasks. You definitely don't want just anyone accessing that! A login system acts as a gatekeeper, ensuring that only authorized users can access your app. It's like having a bouncer at a club – they check IDs and make sure only the right people get in.

Without a login system, your web app is essentially wide open. Anyone who knows the URL can access it, which could lead to data breaches, unauthorized modifications, or other nasty stuff. Implementing a login system is a fundamental security practice that protects your app and its users. Plus, it allows you to track who's using your app and what they're doing, which can be helpful for auditing and troubleshooting.

When designing your login system, think about the specific security requirements of your application. Are you dealing with highly sensitive data that requires multi-factor authentication? Or is a simple username/password combination sufficient? Consider the potential risks and choose a login method that provides an appropriate level of security. It's always better to err on the side of caution when it comes to security. Also, remember to regularly review and update your login system to address any new vulnerabilities or threats that may emerge. Security is an ongoing process, not a one-time fix.

Essential Steps to Create Login System

So, how do we actually build a login system using Google Apps Script? Here are the core steps. I will elaborate more in following sections.

  1. Create a User Database: You'll need a place to store usernames and passwords. A Google Sheet is a simple option for smaller projects.
  2. Build a Login Form: This is the HTML form where users will enter their credentials.
  3. Write the Server-Side Script: This script will handle the authentication logic, verifying the user's credentials against the database.
  4. Implement Session Management: Once a user is logged in, you need to keep track of their session so they don't have to log in again on every page.
  5. Secure Your App: Protect against common web vulnerabilities like cross-site scripting (XSS) and SQL injection.

Step 1: Setting Up the User Database

Alright, let's start with the foundation: the user database. For simplicity, we'll use a Google Sheet to store our usernames and passwords. Open up Google Sheets and create a new spreadsheet. Name it something like "User Database" (original, right?). In the first sheet, create the following columns:

  • Username: This will be the user's login name.
  • Password: This will be the user's encrypted password. Never store passwords in plain text!
  • Salt: A random string used to salt the password before hashing. This adds an extra layer of security.

Populate the sheet with a few test users. For the password and salt, we'll generate them using a hashing function later on. For now, just put some placeholders in there. Remember, never store actual passwords directly. Doing so is a massive security risk.

Think of the salt as a unique ingredient that you add to each password before you hash it. This makes it much harder for hackers to crack your passwords, even if they get their hands on your database. Without a salt, all identical passwords would have the same hash, making them easy to identify. By adding a unique salt to each password, you ensure that each hash is unique, even for identical passwords. This significantly increases the security of your system.

Consider adding additional fields to your user database, such as email address, first name, last name, and user role. These fields can be useful for personalizing the user experience and controlling access to different parts of your application. For example, you might want to restrict certain functionality to users with a specific role, such as administrators or moderators. By storing this information in your user database, you can easily implement these types of access controls. Just be sure to store any sensitive information securely, using encryption or other appropriate security measures.

Step 2: Crafting the Login Form

Next up, the login form! This is where users will actually enter their username and password. Create a new HTML file (e.g., login.html) and add the following code:

<!DOCTYPE html>
<html>
<head>
    <title>Login</title>
</head>
<body>
    <h1>Login</h1>
    <form id="loginForm">
        <label for="username">Username:</label><br>
        <input type="text" id="username" name="username"><br><br>

        <label for="password">Password:</label><br>
        <input type="password" id="password" name="password"><br><br>

        <button type="submit">Login</button>
    </form>

    <p id="message"></p>

    <script>
        document.getElementById('loginForm').addEventListener('submit', function(e) {
            e.preventDefault();
            google.script.run
                .withSuccessHandler(function(result) {
                    document.getElementById('message').textContent = result;
                })
                .login(document.getElementById('username').value, document.getElementById('password').value);
        });
    </script>
</body>
</html>

This is a basic HTML form with fields for username and password, a submit button, and a message area to display login status. The JavaScript code prevents the default form submission and instead calls a Google Apps Script function called login with the username and password as arguments. The withSuccessHandler function will display the result returned by the login function in the message area.

Consider adding some styling to your login form to make it more visually appealing. You can use CSS to customize the appearance of the form elements, such as the input fields, labels, and buttons. You can also add a background image or color to make the form more engaging. A well-designed login form can improve the user experience and make your application more professional. Just be sure to keep the design clean and simple, and avoid using distracting animations or effects.

Implement client-side validation to ensure that the user enters valid data before submitting the form. For example, you can check that the username and password fields are not empty, and that the password meets certain complexity requirements, such as a minimum length or a combination of uppercase and lowercase letters. Client-side validation can help prevent errors and reduce the load on your server by catching invalid data before it is sent to the server.

Step 3: Building the Server-Side Script

Now, let's create the Google Apps Script that will handle the login logic. Open your Google Sheet and go to "Tools" > "Script editor". Replace the default code with the following:

const SHEET_ID = 'YOUR_SHEET_ID'; // Replace with your sheet ID

function doGet(e) {
  return HtmlService.createHtmlOutputFromFile('login')
      .setSandboxMode(HtmlService.SandboxMode.IFRAME)
      .setTitle('Login');
}

function login(username, password) {
  const ss = SpreadsheetApp.openById(SHEET_ID);
  const sheet = ss.getSheetByName('Sheet1'); // Or whatever your sheet is named
  const data = sheet.getDataRange().getValues();

  // Find the user
  for (let i = 1; i < data.length; i++) { // Start from 1 to skip the header row
    if (data[i][0] === username) {
      // User found! Now verify the password
      const salt = data[i][2];
      const hashedPassword = data[i][1];
      const attemptedHash = generateHash(password, salt);

      if (attemptedHash === hashedPassword) {
        // Login successful!
        // TODO: Implement session management here
        return 'Login successful!';
      } else {
        return 'Incorrect password.';
      }
    }
  }

  return 'User not found.';
}

function generateHash(password, salt) {
  const saltedPassword = salt + password;
  const hash = Utilities.computeDigest(Utilities.DigestAlgorithm.SHA_256, saltedPassword);
  const hashString = hash.map(byte => (
    (byte < 0 ? byte + 256 : byte).toString(16).padStart(2, '0')
  )).join('');
  return hashString;
}

function generateSalt() {
  return Utilities.base64Encode(Utilities.computeDigest(Utilities.DigestAlgorithm.SHA_256, Math.random().toString())).substring(0, 16);
}

function test() {
  Logger.log(generateSalt());
}

Replace 'YOUR_SHEET_ID' with the actual ID of your Google Sheet. You can find the sheet ID in the URL of your spreadsheet.

This script does the following:

  • doGet(e): This function serves the login.html file when the web app is accessed.
  • login(username, password): This function is called by the login form. It retrieves the user data from the sheet, compares the entered password (after hashing) with the stored password, and returns a success or failure message.
  • generateHash(password, salt): This function generates a SHA-256 hash of the password, using the provided salt.
  • generateSalt(): This function generates a random salt.

Before deploying the web app, you need to add password and salt to the user database.

function setPassword() {
  const ss = SpreadsheetApp.openById(SHEET_ID);
  const sheet = ss.getSheetByName('Sheet1'); // Or whatever your sheet is named
  const data = sheet.getDataRange().getValues();

  for (let i = 1; i < data.length; i++) { // Start from 1 to skip the header row
    const salt = generateSalt();
    const password = 'password' + i;
    const hashedPassword = generateHash(password, salt);
    sheet.getRange(i + 1, 2).setValue(hashedPassword);
    sheet.getRange(i + 1, 3).setValue(salt);
    Logger.log('password:' + password);
    Logger.log('salt:' + salt);
    Logger.log('hashedPassword:' + hashedPassword);
  }
}

Run the function setPassword. Then you can deploy the web app. To deploy the web app, go to "Deploy" > "New deployment". Configure the deployment settings:

  • Select type: Web app
  • Description: (Optional) Add a description.
  • Who has access: Choose "Anyone" or "Anyone with Google account" depending on your requirements.

Click "Deploy". You'll be prompted to authorize the script. Once authorized, you'll get a URL for your web app. Open this URL in your browser, and you should see the login form.

Enhance the login function to handle different types of authentication, such as multi-factor authentication or social login. Multi-factor authentication adds an extra layer of security by requiring users to provide multiple forms of identification, such as a password and a verification code sent to their phone. Social login allows users to log in using their existing accounts on social media platforms like Google or Facebook. By supporting multiple authentication methods, you can provide a more secure and convenient login experience for your users.

Consider adding error handling to your server-side script to gracefully handle unexpected errors or exceptions. For example, you can use try-catch blocks to catch potential errors and log them for debugging purposes. You can also display user-friendly error messages to the user in case of an error. Proper error handling can help prevent your application from crashing and provide a better user experience.

Step 4: Implementing Session Management

Okay, so now you can log in, but you'll notice that if you navigate away from the page, you're immediately logged out. That's because we haven't implemented session management yet. Session management allows you to keep track of logged-in users so they don't have to re-enter their credentials on every page.

Unfortunately, Google Apps Script doesn't have built-in session management. You'll need to implement it yourself. One common approach is to use the CacheService to store session data.

Here's how you can modify the login function to use the CacheService:

function login(username, password) {
  const ss = SpreadsheetApp.openById(SHEET_ID);
  const sheet = ss.getSheetByName('Sheet1'); // Or whatever your sheet is named
  const data = sheet.getDataRange().getValues();
  const cache = CacheService.getScriptCache();

  // Find the user
  for (let i = 1; i < data.length; i++) {
    if (data[i][0] === username) {
      // User found! Now verify the password
      const salt = data[i][2];
      const hashedPassword = data[i][1];
      const attemptedHash = generateHash(password, salt);

      if (attemptedHash === hashedPassword) {
        // Login successful!
        // Store the username in the cache
        cache.put('loggedInUser', username, 3600); // Store for 1 hour (3600 seconds)
        return 'Login successful!';
      } else {
        return 'Incorrect password.';
      }
    }
  }

  return 'User not found.';
}

And here's how you can check if a user is logged in on other pages:

function isLoggedIn() {
  const cache = CacheService.getScriptCache();
  const loggedInUser = cache.get('loggedInUser');
  return loggedInUser !== null;
}

On each page that requires authentication, call the isLoggedIn() function. If it returns true, the user is logged in. If it returns false, redirect them to the login page.

Use secure cookies to store session identifiers. Cookies are small text files that are stored on the user's computer and used to identify the user's session. However, cookies can be vulnerable to security threats if they are not properly protected. To mitigate these risks, you should use secure cookies, which are encrypted and can only be transmitted over HTTPS connections. You should also set the HttpOnly flag on your cookies to prevent them from being accessed by client-side scripts, which can help protect against cross-site scripting (XSS) attacks.

Implement session timeouts to automatically log users out after a period of inactivity. Session timeouts can help prevent unauthorized access to user accounts if a user forgets to log out or leaves their computer unattended. You can implement session timeouts by storing the user's last activity time in the session data and checking it on each request. If the user has been inactive for a certain period of time, you can automatically log them out and clear their session data.

Step 5: Securing Your App

Security is paramount, guys! Here are some essential security practices to keep in mind:

  • Never store passwords in plain text: Always hash passwords using a strong hashing algorithm like SHA-256 or bcrypt.
  • Use a salt: Add a unique salt to each password before hashing to prevent rainbow table attacks.
  • Sanitize user input: Always sanitize user input to prevent XSS attacks. Use the HtmlService.createHtmlOutput() method to escape HTML characters.
  • Use parameterized queries: If you're using a database, use parameterized queries to prevent SQL injection attacks.
  • Keep your code up to date: Regularly update your Google Apps Script project to the latest version to patch any security vulnerabilities.

By following these security practices, you can significantly reduce the risk of security breaches and protect your app and its users.

Implement input validation to prevent malicious code from being injected into your application. Input validation involves checking the data that users enter into your application to ensure that it is valid and does not contain any malicious code. You can use regular expressions or other validation techniques to check the format and content of user input. By validating user input, you can prevent attackers from injecting malicious code into your application and compromising its security.

Monitor your application for suspicious activity and security breaches. Regular monitoring can help you detect and respond to security incidents in a timely manner. You can use logging and auditing tools to track user activity and identify suspicious patterns. You can also set up alerts to notify you of potential security breaches, such as unauthorized access attempts or unusual data modifications. By monitoring your application for suspicious activity, you can quickly identify and address security threats before they cause significant damage.

Conclusion

And there you have it! A basic login system for your Google Apps Script web app. This is just a starting point, of course. You can customize it to fit your specific needs and security requirements. Remember to always prioritize security and keep your code up to date.