Are there any specific PHP functions or libraries that can help prevent users from logging in multiple times with the same credentials?

To prevent users from logging in multiple times with the same credentials, you can use a session-based approach where a unique identifier is generated upon successful login and stored in the user's session. Subsequent login attempts with the same credentials can be checked against this identifier to prevent multiple logins. 

session_start();

// Check if user is already logged in
if(isset($_SESSION['logged_in']) && $_SESSION['logged_in'] === true){
    // Redirect user to home page or display an error message
    header("Location: home.php");
    exit;
}

// Validate user credentials
if($username === 'example' && $password === 'password'){
    // Generate a unique identifier
    $unique_id = uniqid();
    
    // Store the unique identifier in the session
    $_SESSION['unique_id'] = $unique_id;
    
    // Set logged_in flag to true
    $_SESSION['logged_in'] = true;
    
    // Redirect user to home page
    header("Location: home.php");
    exit;
} else {
    // Display error message
    echo "Invalid username or password";
}

Keywords

PHP session management authentication security prevent multiple logins

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