What are common pitfalls when using PHP functions to validate user input, such as passwords and usernames?

Common pitfalls when using PHP functions to validate user input, such as passwords and usernames, include not properly sanitizing input data, not using secure hashing algorithms for passwords, and not properly validating the input against the expected format. To solve these issues, always sanitize user input using functions like `filter_var()`, use secure hashing algorithms like `password_hash()` for passwords, and validate input against expected formats using functions like `preg_match()`. 

// Sanitize user input
$username = filter_var($_POST['username'], FILTER_SANITIZE_STRING);

// Hash password using bcrypt
$password = password_hash($_POST['password'], PASSWORD_DEFAULT);

// Validate email format
if (!filter_var($_POST['email'], FILTER_VALIDATE_EMAIL)) {
    echo "Invalid email format";
}

Keywords

SQL injection XSS attacks password_hash filter_var password_verify

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