gistfile1.php

<?php
$dbh = new PDO('mysql:host=localhost;dbname=test', 'root', 'sten123');

function authenticate($username, $password) {
    global $dbh;

    $loginStmt = $dbh->prepare('SELECT password FROM users WHERE username = :username');
    $loginStmt->bindValue(':username', $username);
    $loginStmt->execute();

    $row = $loginStmt->fetch(PDO::FETCH_ASSOC);

    if (!$row)
        return 'Account not found';

    if (!password_verify($password, $row['password']))
        return 'Incorrect password';

    return null;
}

$error = authenticate('Ineentho', 'sten123');

if ($error) {
    echo 'Could not login: ' . $error;
} else {
    echo 'Logged in';
}