Adding LDAP AuthN and AuthZ in PHP applications is a very easy thing with LDAPAuthPHP.
An usage example (there are a lot of different ways):

<?php
$pageURL = 'http';
if ($_SERVER["HTTPS"] == "on") {        
    $pageURL .= "s";    
}       
$pageURL .= "://";      
if ($_SERVER["SERVER_PORT"] != "80") {  
    $pageURL .= $_SERVER["SERVER_NAME"].":
".$_SERVER["SERVER_PORT"].$_SERVER["REQUEST_URI"];    
} else {        
    $pageURL .= $_SERVER["SERVER_NAME"].$_SERVER["REQUEST_URI"];        
}

session_name('MYAPP');  
session_start();        
if (!isset($_SESSION["user"])) {        
    include("LdapAuth.inc.php");        
    $ldap=new LdapAuth();       
    $ldap->setSessionAttr("user","uid");        
    $ldap->setSessionName("MYAPP");     
    $ldap->setRedirectPage($pageURL);
 //page where we get redirected after login (in this case self)
    include("LdapStandalonePageProtector.inc.php");
}       
else { 
  echo "Logged In As: ".$_SESSION["user"]."</hr>";
  //paste here the old page code (or write the new page to protect)
}

• Load balancing and HA beetween multiple LDAP servers
  
• HTML Standalone Page Protector (if you are lazy you don’t need to write a login form)
  
• BasicAuth Standalone Page Protector (wanna LDAP-protect an RSS feed?)
  
• Custom attribute fetching (for AuthZ)
  
• Configurable ldap2Session attribute mapping (LDAP Attr -> PHP Session Attr)
  
• Access logging (to be improved and localized)
  

• php5-ldap (there are .deb and .rpm package in standard main linux distro repositories) ( http://packages.debian.org/sid/php5-ldap )
  
• If you are using LDAPS:// (And i suggest to use it always, a part when the LDAP is on the same machine of the PHP server) you will need to modify /etc/ldap/ldap.conf to set ldap server certificate verification or you will get a blank page using LdapAuthPHP.
  
• I found this php5-ldap certificate validation a little buggy then if you experience problems try to set TLS_REQCERT never (in /etc/ldap/ldap.conf) for skipping the certificate validation but keeping all the benefits of the SSL encryption.