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<?php
session_start();

$userName = $_POST["username"];
$userPass = $_POST["pass"];

$file = file_get_contents("users.json");
$users = json_decode($file, true);

$loging = false;
for ($i = 0; $i < count($users); $i++) {
    if ($users[$i]["username"] == $userName && $users[$i]['password'] == $userPass) {
        $_SESSION['user_id'] = $users[$i]["id"];
        $loging = true;
        header("location:../destination");
    }
}
if (!$loging)
    // echo "Username or password is invalid";
    header("location:../login.php?log=false");