<?php
$connection = mysqli_connect(
    "localhost",
    "root",
    "",
    "mydb"
);

if (mysqli_connect_errno()) {
    exit('failed to connect to the database server.');
}

if (!isset($_GET['auth_username']) || !isset($_GET['auth_password'])) {
    exit('you failed to provide the correct parameters.');
}

$username = isset($_GET['auth_username']) ? $_GET['auth_username'] : '';
$password = isset($_GET['auth_password']) ? $_GET['auth_password'] : '';

$commandText = "SELECT `password`,`has_subscription` FROM `a__client_accounts`";
$whereClause = "WHERE `username` = '" . $username . "'";
$result = $connection->query($commandText . " " . $whereClause);

if (!$result) {
    exit('Invalid query: ' . $connection->error);
}
else if ($result->num_rows > 0) {
    $array =  $result->fetch_array();

    if (!password_verify($password, $array['password'])) {
        exit('we found your account, but you entered the wrong password.');
    }
    else if ($array['has_subscription'] == '0') {
        exit('you authenticated, but you don't have a subscription');
    }
    else {
        exit('congratulations');
    }
}
else {
    echo 'no account was found with that name.';
}