PHP DB Request for Astra Auth.

<?php

$db_host = "127.0.0.1";
$db_name = "db";
$db_user = "user";
$db_pass = "****";

if(!isset($_GET["key"])) {
    header("HTTP/1.0 403 Forbidden");
    echo("Undefined key" . PHP_EOL);
    exit;
}

$link = mysqli_connect($db_host, $db_user, $db_pass, $db_name);

if(mysqli_connect_errno()) {
    header("HTTP/1.0 403 Forbidden");
    echo(mysqli_connect_error() . PHP_EOL);
    exit;
}

$key = mysqli_real_escape_string($link, $_GET["key"]);
$result = mysqli_query($link, "SELECT id FROM users WHERE key='" . $key . "'");
if(!$result || !$result->num_rows) {
    header("HTTP/1.0 403 Forbidden");
    echo("Key not found" . PHP_EOL);
    mysqli_close($link);
    exit;
}

echo("Ok");

mysqli_free_result($result);
mysqli_close($link);

?>