Authenticating user using LDAP from PHP

Question

The general procedure would be (relevant ext/ldap php commands in brackets):

1. connect to LDAP server using the "LDAP Host" and "LDAP port no" (ldap_connect()) and set the correct connection options (ldap_set_option()), especially LDAP_OPT_PROTOCOL_VERSION and LDAP_OPT_REFERRALS

2. bind to LDAP server using the "LDAP account to bind" and "LDAP account password" (ldap_bind()) - if you're authenticating against an Active Directory server you can directly use the username and password from the login page and skip all the following steps.

3. search the tree for a matching user entry/object by specifing the "BASE DN" and the appropriate LDAP filter - most likely something like (&(objectClass=user)(sAMAccountName=%s)) where %s should be replaced by the username to be authenticated (ldap_search())

4. check if the number of returned entries is 1 (if <> 1 then something has gone wrong, e.g. no user found or multiple users found)

5. retrive the distinguished name (DN) of this single entry (ldap_get_dn())

6. use the DN found in the last step to try to bind to the LDAP server with the password given at the authentication page (ldap_bind())

7. if the bind succeeds then everything is OK, if not, most likely the password is wrong

It's really not as hard as it sounds at first. Generally I'd propose to use some sort of standard library for authenticating against a LDAP server such as the Net_LDAP2 PEAR package or Zend_Ldap out of the Zend Framework. I have no experience with actually using Net_LDAP2 (although I know the code quite well) but Zend_Ldap works very well against Active Directory servers or ADAMS servers (which is obviously what you're working with).

This will do the trick using Zend_Ldap:

$options = array(
    'host'                 => 'ad.blueroom.ac.uk',
    'useStartTls'          => true,
    'accountDomainName'    => 'blueroom.ac.uk',
    'accountCanonicalForm' => 4,
    'baseDn'               => 'ou=bluebird,dc=bluebird,dc=ac,dc=my',
);
$ldap = new Zend_Ldap($options);
try {
    $ldap->bind('user', 'password');
} catch (Zend_Ldap_Exception $e) {
    // something failed - inspect $e
}
// bind successful
$acctname = $ldap->getCanonicalAccountName('user', Zend_Ldap::ACCTNAME_FORM_DN);

You might try http://code.activestate.com/recipes/101525/ while referring to http://us3.php.net/ldap and other results from a Google search for [php ldap authentication].

@Stephen provided good points. Here is my plain PHP code to authenticate using AD:

1. first you need to know this parameters: server host, user domain (you need also base dn if you want query AD).

2. use the following code:

   $ldap = ldap_connect($host); // e.g. 165.5.54.6 or an URL
   ldap_set_option($ldap, LDAP_OPT_PROTOCOL_VERSION, 3); // Recommended for AD
   ldap_set_option($ldap, LDAP_OPT_REFERRALS, 0);
   $bind = ldap_bind($ldap, $username.'@'.$userDomain, $passwrod);
   
   if($bind){
   // successful authentication. 
   }
   

you could use http://pear.php.net/package/Net_LDAP2/docs it's nice and works.

Example of connection taken by the doc:

// Inclusion of the Net_LDAP2 package:
require_once 'Net/LDAP.php';

// The configuration array:
$config = array (
    'binddn'    => 'cn=admin,ou=users,dc=example,dc=org',
    'bindpw'    => 'password',
    'basedn'    => 'dc=example,dc=org',
    'host'      => 'ldap.example.org'
);

// Connecting using the configuration:
$ldap = Net_LDAP2::connect($config);

// Testing for connection error
if (PEAR::isError($ldap)) {
    die('Could not connect to LDAP-server: '.$ldap->getMessage());
}