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Overview

In this quickstart, you’ll add Fingerprint to a PHP server to prevent fraudulent account creation. The example use case we’ll use for this quickstart is stopping new account fraud, where attackers create multiple fake accounts to abuse promotions, exploit systems, or evade bans. However, the steps you’ll follow apply to most use cases. You can flag and block suspicious users by identifying the device behind each sign-up attempt, login, or transaction. In this quickstart, you’ll learn how to:
  • Set up a PHP server with a Fingerprint integration
  • Retrieve visitor identification data using the Server API
  • Block bots and suspicious devices
  • Prevent multiple signups from the same device
This guide focuses on the back-end integration and must be completed after identifying a visitor and generating a request ID. Before starting this quickstart, start with one of our front-end or mobile quickstarts to see how to identify a visitor in your front-end.
Estimated time: < 10 minutes

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Prerequisites

Before you begin, make sure you have the following:
  • PHP 8.0 or later
  • Composer (PHP package manager) installed
  • SQLite3 installed
  • A completed front-end or mobile Fingerprint implementation (See our quickstarts)

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1. Get your secret API key

Before starting this quickstart, you should already have a front-end Fingerprint implementation that sends the requestId to your server. If not, pause here and check out one of our front-end or mobile quickstarts first.
If you’re ready:
  1. Sign in and go to the API keys page in the Fingerprint dashboard.
  2. Create a new secret API key.
  3. Copy it somewhere safe so you can use it to retrieve full visitor identification data from the Server API.

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2. Set up your project

We’ll start by creating a PHP server that exposes a POST endpoint for account creation. If you already have a project you want to use, skip to the next section.
  1. Create a project folder, move into it, and set up Composer with the required packages:
Terminal
mkdir fingerprint-php-quickstart && cd fingerprint-php-quickstart
composer init -n --name="demo/fp-php" --type=project
composer require fingerprint/fingerprint-pro-server-api-sdk vlucas/phpdotenv
  1. Create a .env file to store your Fingerprint secret API key (replace with your actual key):
Terminal
FINGERPRINT_SECRET_API_KEY=your_secret_key_here
  1. Create a new file called index.php and load your dependencies:
index.php
<?php
require __DIR__ . '/vendor/autoload.php';

use Dotenv\Dotenv;

$dotenv = Dotenv::createImmutable(__DIR__);
$dotenv->load();
  1. Then create a POST route for /api/create-account. For now, this will just return a placeholder message so you can confirm the server is running:
index.php
$path = parse_url($_SERVER['REQUEST_URI'], PHP_URL_PATH);

if ($_SERVER['REQUEST_METHOD'] === 'POST' && $path === '/api/create-account') {
    header('Content-Type: application/json');
    echo json_encode(['status' => 'Account created!']);
    exit;
}

http_response_code(404);
header('Content-Type: application/json');
echo json_encode(['error' => 'Not found']);

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3. Initialize Fingerprint and retrieve visitor data

Now you’ll configure the Fingerprint server SDK using your secret API key and use it to fetch detailed visitor data for each signup attempt. When making the initial visitor identification request in the front end, you received a requestId. This ID is unique to each identification event. Your server can then use the Fingerprint Events API to retrieve complete identification data, including the trusted visitor ID and other actionable insights like whether they are using a VPN or are a bot.
  1. Import the Fingerprint SDK classes and the Guzzle HTTP client at the top of index.php (after your other use statements):
index.php
use Fingerprint\ServerAPI\Api\FingerprintApi;
use Fingerprint\ServerAPI\Configuration;
use GuzzleHttp\Client as HttpClient;
  1. Initialize the Fingerprint client using your secret API key and your specific workspace region. (After loading your .env variables):
index.php
$config = Configuration::getDefaultConfiguration($_ENV['FINGERPRINT_SECRET_API_KEY'], Configuration::REGION_GLOBAL);
$fp = new FingerprintApi(new HttpClient(), $config);
  1. In your /api/create-account route, retrieve the inputs sent from your front end and fetch the full visitor identification details with getEvent():
index.php
$path = parse_url($_SERVER['REQUEST_URI'], PHP_URL_PATH);

if ($_SERVER['REQUEST_METHOD'] === 'POST' && $path === '/api/create-account') {
    header('Content-Type: application/json');

    $input = json_decode(file_get_contents('php://input'), true) ?? [];
    $username  = $input['username']  ?? null;
    $password  = $input['password']  ?? null;
    $requestId = $input['requestId'] ?? null;

    if (!$username || !$password || !$requestId) {
        http_response_code(400);
        echo json_encode(['error' => 'Missing required fields.']);
        exit;
    }

    try {
        // Retrieve full identification details for this request
        [$model, $response] = $fp->getEvent($requestId);
        $event = json_decode($response->getBody()->getContents());
    } catch (Throwable $e) {
        http_response_code(500);
        error_log("Error retrieving event: " . $e->getMessage());
        echo json_encode(['error' => 'Failed to create account.']);
        exit;
    }

    echo json_encode(['status' => 'Account created!']);
    exit;
}
Using the requestId the Fingerprint server client will retrieve the full data for the visitor identification request. The returned object will contain the visitor ID, IP address, device and browser details, and Smart Signals like bot detection, incognito mode detection, and detections for VPN or virtual machine use. You can see a full example of the event structure, and test it with your own device, in our demo playground. For additional checks to ensure the validity of the data coming from your front end view how to protect from client-side tampering and replay attacks in our documentation.

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4. Block bots and suspicious devices

This optional step uses the Bot Detection Smart Signal which is available only on paid plans.
A simple but powerful way to prevent fraudulent account creation is to block automated signups that come from bots. The event object includes the Bot Detection Smart Signal that flags automated activity, making it easy to reject bot traffic.
  1. Continuing in your /api/create-account route, after the try/catch where you fetch the event, extract the bot detection signal and decide whether to allow the signup:
index.php
$botResult = $event->products->botd->data->bot->result;

// Block automated signups
if ($botResult !== 'notDetected') {
    error_log("Account creation blocked: bot detection result = {$botResult}");
    http_response_code(403);
    echo json_encode(['error' => 'Failed to create account.']);
    exit;
}
This signal returns good for known bots like search engines, bad for automation tools, headless browsers, or other signs of automation, and notDetected when no bot activity is found. You can also layer in other Smart Signals to catch more suspicious devices. For example, you can use Fingerprint’s Suspect Score to determine when to add additional friction to create an account.

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5. Prevent multiple signups from the same device

To catch repeated signups from the same device, you can use the visitorId from the Fingerprint identification event. By saving this ID alongside each created account, you can easily detect and block duplicate signups from the same device. For this quickstart, we’ll use SQLite because it’s a simple to use database with little setup.
  1. Create a file called setup.php with the following code to initialize a simple SQLite table:
setup.php
<?php
$db = new PDO('sqlite:database.sqlite');
$db->exec("
CREATE TABLE IF NOT EXISTS accounts (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    username TEXT NOT NULL,
    password TEXT NOT NULL,
    visitorId TEXT NOT NULL
)");
echo "Database ready.";
  1. Run the script once to create the database file and table:
Terminal
php setup.php
  1. In index.php, open a SQLite connection after loading your environment variables:
index.php
$db = new PDO('sqlite:database.sqlite');
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
  1. In your /api/create-account route, after the bot check, extract the trusted visitor ID from the event:
index.php
$visitorId = $event->products->identification->data->visitorId;
  1. Check if this device has already created an account:
index.php
$check = $db->prepare("SELECT COUNT(*) FROM accounts WHERE visitorId = ?");
$check->execute([$visitorId]);
$alreadyExists = $check->fetchColumn() > 0;

if ($alreadyExists) {
    http_response_code(429);
    error_log("Account already exists: visitorId = {$visitorId}");
    echo json_encode(['error' => 'Failed to create account.']);
    exit;
}
  1. Insert the new account with the visitor ID and return success:
index.php
$insert = $db->prepare("INSERT INTO accounts (username, password, visitorId) VALUES (?, ?, ?)");
$insert->execute([$username, $password, $visitorId]);

echo json_encode(['status' => 'Account created!']); // Was already there
exit; // Was already there
This gives you a basic system to detect and block repeat signups. You can expand on this by allowing a limited number of accounts per device, adjusting your response based on business rules, only evaluating recent signups, etc.
This is a minimal example to show how to use the Fingerprint SDK. In a real application, make sure to implement proper security practices, especially around password handling and storage.

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6. Test your implementation

Now that everything is set up, you can test the full flow using your existing front end.

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Before you test

If your front end is running on a different port (like localhost:5173 or localhost:3000), you may run into CORS issues for testing. To quickly fix this for local development & testing:
  1. Add the following at the top of index.php, right after your require and use statements:
header("Access-Control-Allow-Origin: *");
header("Access-Control-Allow-Methods: POST, OPTIONS");
header("Access-Control-Allow-Headers: Content-Type");

if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
    http_response_code(204);
    exit;
}

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Test the implementation

  1. Start your PHP server:
Terminal
php -S localhost:8000
  1. In your front end, trigger a sign-up request that sends the requestId, username, and password to your server’s /api/create-account endpoint. To see the reply messages make sure to parse and display or console log the response from your server.
  2. Within your front end, input a username and password to create a user. Then try to create another user and see that the second attempt will be rejected.
  3. Bonus: Try creating an account using a headless browser.

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Next steps

You now have a working back-end fraud check using Fingerprint. From here, you can expand your logic with more Smart Signals, adjust thresholds based on your risk tolerance, or introduce additional checks for suspicious users. These same techniques apply to a wide range of fraud prevention use cases, from detecting fake reviews to blocking payment abuse or preventing account takeovers. To go further, check out our use case tutorials for step-by-step guides tailored to specific problems you can solve with Fingerprint. Check out these related resources: