You create a file with the name login.php, with following contents:

<?php

$user = "test";
$pw = "12345";

function authenticate () {
  Header("WWW-authenticate: basic realm=\"Restricted Area\"");
  Header("HTTP/1.0 401 Unauthorized");
  echo "Restricted Area!";
  exit;
}

if (!isset($_SERVER['PHP_AUTH_USER']) || $_SERVER['PHP_AUTH_USER'] != $user || $_SERVER['PHP_AUTH_PW'] != $pw) {
  authenticate();
}
?>

Then you have to include the login.php to the top of index.php:

<?php
  include ("login.php");
?>

Thats all! It is important that there are no other index.* files in the directory.

So, now about our problem. We want make our application working in all browsers, because it’s good to make it work everywhere. So we have to aks the user agent (basically the client program, not the agent Smith from Matrix), what browser are you using? And we want make it so flexible, that we can ask him this every time. For this purpose we introduce a function:

function getBrowser()
{
  $ua = $_SERVER['HTTP_USER_AGENT']
  if (strstr($ua,'Opera')) {  // Opera
    $browser = ereg_replace(".+\(.+\) (Opera |v){0,1}([0-9,\.]+)[^0-9]*","Opera\\2",$ua);
    if(ereg('^Opera/.*',$ua)) {
      $browser = ereg_replace("Opera/([0-9,\.]+).*","Opera \\1",$ua);
    }
  } elseif (strstr($ua,'MSIE')) { // MSIE
    $browser=ereg_replace(".+\(.+MSIE ([0-9,\.]+).+", "Internet Explorer \\1",$ua);
  } elseif (strstr($ua,'Firefox')) { // Firefox
    $browser=ereg_replace(".+\(.+rv:.+\).+Firefox/(.*)", "Firefox \\1", $ua);
  } elseif (strstr($ua,'Mozilla')) {  //  Mozilla
    $browser=ereg_replace(".+\(.+rv:([0-9,\.]+).+","Mozilla \\1",$ua);
  } else {  // None of them.
    $browser=$ua;
  }
  return $browser;
}

If we want our PHP script to show us the browser, we write:

echo(getBrowser());

Now we can see, what kind of browser is used and use it in our aplication:

if (getBrowser() == 'Internet Explorer 6.0') {
echo ("Please install another Browser");
}

Thats it!