从XML读取凭证并初始化变量

我正在尝试从xml中读取凭证，并使用php初始化为私有变量。

<?xml version="1.0" encoding="ISO-8859-1"?>
<config>
    <host>localhost</host>
    <username>Jani</username>
    <password>1234r</password>
</config>

我使用下面的类和构造函数来初始化变量。

<?php
class Admin {
    public $host = "";
    private $username;
    private $password;
    private $table;
    private $crendentials = array();
    public function __construct() {
    $xml = simplexml_load_file("config.xml");
    foreach ($this->crendentials as $key => $value) {
        if ($key == $this->host) {
            $this->host = $value;
        } elseif ($key == $this->username) {
            $this->username = $value;
        } elseif ($key == $this->password) {
            $this->password = $value;
        }
    }

    foreach ($xml->children() as $child) {
        $this->crendentials[$child->getName()] = $child;
    }
}
public function getHost() {
    print_r($this->crendentials);
    echo $this->host;
    echo $this->username;
    echo $this->password;
}
}
$obj = new Admin;
$obj->getHost();
?>

没有初始化变量。除此之外，还有什么好方法来加载凭据吗?我正在创建一个cms。我做了一些研究，比如使用ini文件。但是我认为xml是最简单的。