Consulta del Active Directory con la extensión Ldap:
<?php
        $ldap_dn = 'xxx@miempresa.com';
	$ldap_password = 'xxx';       
	$ldap_con = ldap_connect("x.miempresa.com",389)  or die ("No ha sido posible conectarse al servidor");            
        if ($ldap_con){
            ldap_set_option($ldap_con, LDAP_OPT_REFERRALS, 0); 
            ldap_set_option($ldap_con, LDAP_OPT_PROTOCOL_VERSION, 3);
            $r=ldap_bind($ldap_con,$ldap_dn,$ldap_password) or die("Couldn't bind to AD!");
        if ($r)
            {            
            //$atributos=array('samaccountname', 'userprincipalname', 'displayname',"mail","memberof","department","displayname","telephonenumber","primarygroupid","objectsid");
            $atributos = array('samaccountname');
            $filtro='(&(objectClass=user)(objectCategory=person)(cn=*))';
            $res=ldap_search($ldap_con,"dc=miempresa,dc=com",$filtro) ;
            $num_entradas=ldap_count_entries($ldap_con, $res);
            $entradas=ldap_get_entries($ldap_con, $res);
           
            foreach($entradas as $i){            
                foreach($atributos as $j){  ?>
                    <?php $array=array($i[$j][0]);
                } 
            }            
            }
        }
        ldap_close($ldap_con);
?>
<th>
                <?php echo $form->labelEx($model,'usuariosolicitante'); ?>                
                <select name="usuariosolicitante" id="usuariosolicitante">
                <option selected="selected">Usuario</option>
                <?php
                foreach($entradas as $i){
                  foreach($atributos as $j) { 
                      $array=array($i[$j][0]);?>
                    <option value="<?= $i[$j][0] ?>"><?= $i[$j][0] ?></option>
                <?php
</th>
                }
                }?>