What are some potential pitfalls of allowing users to register through an existing user in PHP?

One potential pitfall of allowing users to register through an existing user in PHP is the risk of creating duplicate accounts or impersonation. To solve this issue, you can implement a check to verify if the email or username provided during registration already exists in the database before allowing the user to proceed with the registration process. 

// Check if the email or username already exists in the database
$email = $_POST['email'];
$username = $_POST['username'];

$query = "SELECT * FROM users WHERE email = '$email' OR username = '$username'";
$result = mysqli_query($connection, $query);

if(mysqli_num_rows($result) > 0) {
    // Display an error message and prevent registration
    echo "Email or username already exists. Please choose a different one.";
} else {
    // Proceed with the registration process
    // Insert user data into the database
}

Keywords

SQL injection session hijacking cross-site scripting user impersonation data leakage

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