Http authentication not working in linux hosted website
<?php
 // User name and password for authentication

$username='username';
$password='password';


if (!isset($_SERVER['PHP_AUTH_USER']) || !isset($_SERVER['PHP_AUTH_PW']) ||
($_SERVER['PHP_AUTH_USER'] !=$username) || ($_SERVER['PHP_AUTH_PW'] !=$password))
{
 // The user name/password are incorrect so send the authentication headers
   header('HTTP/1.1 401 Unauthorized');
  header('WWW-Authenticate: Basic realm="My Web Page:The Freedom Square Of Internet"');
  exit('<h2>My Web page</h2>Sorry, you must enter a valid user name and password to access this page.');
  }
?>

RewriteCond %{HTTP:Authorization} ^(.+)
RewriteRule ^(.*)$ $1 [E=HTTP_AUTHORIZATION:%1,PT]