djpw-faq-login.php

## djpw-faq-login.php
<?php
// global variables
$pathIndex = 'http://' . $_SERVER['SERVER_NAME'] . $_SERVER['PHP_SELF'];
$connection = mysqli_connect('localhost', 'root', '', 'muj_projekt');
mysqli_set_charset($connection, 'utf8');

session_start();


/**
 * Attemps to log-in the user.
 *
 * @param  string $username
 * @param  string $password (in plain text)
 * @return bool   TRUE for success, FALSE otherwise
 */
function userLogin($username, $password)
{
	global $connection;
	$result = mysqli_query($connection, '
		SELECT *
		FROM `users`
		WHERE `name` = "' . mysqli_real_escape_string($connection, $username) . '"'
	);
	$row = mysqli_fetch_assoc($result);

	if ($row === NULL) {
		return FALSE; // incorrect username
	}

	if (!password_verify($password, $row['password'])) {
		return FALSE; // incorrect password
	}

	session_regenerate_id(TRUE); // prevents session fixation
	unset($row['password']);
	$_SESSION['user'] = $row;
	return TRUE;
}


/**
 * Logouts the user.
 *
 * @return void
 */
function userLogout()
{
	unset($_SESSION['user']);
}


/**
 * Handles log-in request.
 *
 * @return void
 */
function actionLogin()
{
	global $pathIndex;
	$ok = userLogin($_POST['username'], $_POST['password']);
	$url = $pathIndex . ($ok ? '' : '?incorrect_login=1');
	header("Location: $url", TRUE, 303);
	exit;
}


/**
 * Handles log-out request.
 *
 * @return void
 */
function actionLogout()
{
	global $pathIndex;
	userLogout();
	header("Location: $pathIndex", TRUE, 303);
	exit;
}

if (isset($_POST['username'], $_POST['password'])) {
	actionLogin($pathIndex);
} elseif (isset($_GET['logout'])) {
	actionLogout($pathIndex);
}
?>
<!doctype html>
<meta charset="utf-8">

<?php if (isset($_SESSION['user'])): ?>
	<p>
		Přihlášen: <?=htmlspecialchars($_SESSION['user']['name']) ?> (id <?=$_SESSION['user']['id'] ?>)
		<a href="<?=htmlspecialchars("$pathIndex?logout=1") ?>">odhlásit</a>
	</p>

<?php else: ?>
	<div>
		<?php if (isset($_GET['incorrect_login'])): ?>
			<p style="color: #F00">Zadali jste neplatné uživatelské jméno nebo heslo</p>
		<?php endif; ?>
		<form action="index.php" method="post">
			Jméno: <input name="username" type="text"><br>
			Heslo: <input name="password" type="password"><br>
			<input name="submit" type="submit" value="Přihlásit">
		</form>
	</div>
<?php endif; ?>