A sample code of user authentication with LDAP from PHP

ldap.php

<?php
// LDAP settings
const LDAP_HOST = "ldap-host";
const LDAP_PORT = 389;
const LDAP_DC = "dc=example,dc=com";
const LDAP_CN = "admin";
const LDAP_PASS = "password";

// Connect
$ldap_conn = ldap_connect(LDAP_HOST, LDAP_PORT);
if (!$ldap_conn) {
    exit('Could not connect to LDAP server.');
}

// Switch protocol to LDAPv3
ldap_set_option($ldap_conn, LDAP_OPT_PROTOCOL_VERSION, 3);
ldap_set_option($ldap_conn, LDAP_OPT_REFERRALS, 0);

// Bind
$ldap_dn = 'cn=' . LDAP_CN . ',' . LDAP_DC;
$ldap_bind = ldap_bind($ldap_conn, $ldap_dn ,LDAP_PASS);
if ($ldap_bind) {
    exit('LDAP bind successful..');
} else {
    exit('LDAP bind failed.');
}