HTTP Authentication

<?php
class httpauth{
  private $realm;
  private $username;
  private $password;
  public function __construct($realm, $sub1, $sub2 = NULL){
    if(is_string($sub1) && is_string($sub2)){
      while($sub1 != $_SERVER['PHP_AUTH_USER'] || $_SERVER['PHP_AUTH_PW'] != $sub2){
        header('WWW-Authenticate: Basic realm="'.$realm.'"');
        die('Invalid Username/Password');
      }
    }else if(is_array($sub1) && is_null($sub2)){
      while(!array_key_exists($_SERVER['PHP_AUTH_USER'], $sub1) || $sub1[$_SERVER['PHP_AUTH_USER']] != $_SERVER['PHP_AUTH_PW']){
        header('WWW-Authenticate: Basic realm="'.$realm.'"');
        die('Invalid Username/Password');
      }
    }else{
      throw new exception('Invalid httpauth parameter types');
    }
    $this->realm = $realm;
    $this->username = $_SERVER['PHP_AUTH_USER'];
    $this->password = $_SERVER['PHP_AUTH_PW'];    
  }
  public function getRealm(){
    return $this->realm;
  }
  public function getUsername(){
    return $this->username;
  }
  public function getPassword(){
    return $this->password;
  }
}