servnest/auth.php

<?php

define("USERNAME_REGEX", "^[a-z]{4,32}$");
define("PASSWORD_REGEX", "^(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])[a-zA-Z0-9]{8,1024}|.{10,1024}$");

// Password storage security
define("ALGO_PASSWORD", PASSWORD_ARGON2ID);
define("OPTIONS_PASSWORD", array(
	"memory_cost" => 65536,
	"time_cost" => 24,
	"threads" => 64,
));

function checkPasswordFormat($password) {
	if (preg_match("/" . PASSWORD_REGEX . "/", $password) !== 1)
		userError("Password malformed.");
}

function checkUsernameFormat($username) {
	if (preg_match("/" . USERNAME_REGEX . "/", $username) !== 1)
		userError("Username malformed.");
}

function hashPassword($password) {
	return password_hash($password, ALGO_PASSWORD, OPTIONS_PASSWORD);
}

function userExist($username) {
	$usernameArray[0] = $username;

	$db = new PDO('sqlite:' . DB_PATH);

	$op = $db->prepare('SELECT username FROM users WHERE username = ?');
	$op->execute($usernameArray);

	$data = $op->fetch();
	if (isset($data['username']))
		return true;
	else
		return false;
}

function checkPassword($username, $password) {
	$username2[0] = $username;

	$db = new PDO('sqlite:' . DB_PATH);

	$op = $db->prepare('SELECT username, password FROM users WHERE username = ?');
	$op->execute($username2);

	$dbPassword = $op->fetch()['password'];

	return password_verify($password, $dbPassword);
}

function outdatedPasswordHash($username) {
	$username2[0] = $username;

	$db = new PDO('sqlite:' . DB_PATH);

	$op = $db->prepare('SELECT username, password FROM users WHERE username = ?');
	$op->execute($username2);

	$dbPassword = $op->fetch()['password'];

	return password_needs_rehash($dbPassword, ALGO_PASSWORD, OPTIONS_PASSWORD);
}

function changePassword($username, $password) {
	$password = hashPassword($password);

	$db = new PDO('sqlite:' . DB_PATH);

	$stmt = $db->prepare("UPDATE users SET password = :password WHERE username = :username");

	$stmt->bindParam(':username', $username);
	$stmt->bindParam(':password', $password);

	$stmt->execute();
}