add attribute to admin user

Question

I need to add a field that I did to the customer, but also to the admin user. I have the customer one working,

$installer->addAttribute('customer', 'ldap_user', array(
    'type'         => 'int',
    'input'        => 'select',
    'source'       => 'eav/entity_attribute_source_boolean',
    'label'             => 'Has AD account',
    'visible'           => true,
    'required'          => false,
));
$attr = Mage::getSingleton( 'eav/config' )->getAttribute( 'customer', 'ldap_user' );
$attr->setData( 'used_in_forms', array( 'adminhtml_customer' ) );
$attr->save();

But I can't seem to find anything on how to do one for the admin user and all attempts so far to convert this to the admin/user model has failed. Any ideas on the correct way to add this field?

*UPDATE Base on @Marius answer I'm closer. The install part works, and the column was added. The tab prepare Form is not yes right. I put

\app\code\local\Wsu\NetworkSecurities\Block\Adminhtml\Permissions\User\Edit\Tab\Main.php

<?php
class Wsu_NetworkSecurities_Block_Adminhtml_Permissions_User_Edit_Tab_Main extends Mage_Adminhtml_Block_Permissions_User_Edit_Tab_Main {

  protected function _prepareForm() {

        parent::_prepareForm();        
        $form = $this->getForm();
        $fieldset = $form->getElements()->searchById('user_base_fieldset');


        $fieldset->addField('ldap_user', 'select', array(
            'name'      => 'is_active',
            'label'     => Mage::helper('adminhtml')->__('LDAP user'),
            'id'        => 'is_active',
            'title'     => Mage::helper('adminhtml')->__('LDAP user'),
            'class'     => 'input-select',
            'style'     => 'width: 80px',
            'options'   => array('1' => Mage::helper('adminhtml')->__('Yes'), '0' => Mage::helper('adminhtml')->__('No')),
        )); 
        $this->setForm($form);

        return $this;

  }

}

But I am not seeing it. I can see also I think I need to rewrite system_account/index too I would think?

/etc/config.xml

<?xml version="1.0" encoding="utf-8"?>
<config>
    <modules>
        <Wsu_NetworkSecurities>
            <version>0.1.0</version>
        </Wsu_NetworkSecurities>
    </modules>
    <global>
        <blocks>
            <wsu_networksecurities>
                <class>Wsu_NetworkSecurities_Block</class>
            </wsu_networksecurities>
    <adminhtml>
        <rewrite>
            <permissions_user_edit_tab_main>Wsu_NetworkSecurities_Block_Adminhtml_Permissions_User_Edit_Tab_Main</permissions_user_edit_tab_main>
        </rewrite>
    </adminhtml>
        </blocks>
    </global>
</config>

That is what I have for the blocks.

UPDATE

So this works to add a new fieldset and add the field, but it never could get in the main fieldset, but it works.

  protected function _prepareForm() {

        parent::_prepareForm();        
        $form = $this->getForm();

        $fieldset = $form->addFieldset('LDAP', array(
            'legend' => Mage::helper('adminhtml')->__('User Info'),
            'class' => 'fieldset-wide'
        ));

        $fieldset->addField('ldap_user', 'select', array(
            'name'      => 'is_active',
            'label'     => Mage::helper('adminhtml')->__('LDAP user'),
            'id'        => 'is_active',
            'title'     => Mage::helper('adminhtml')->__('LDAP user'),
            'class'     => 'input-select',
            'style'     => 'width: 80px',
            'options'   => array('1' => Mage::helper('adminhtml')->__('Yes'), '0' => Mage::helper('adminhtml')->__('No')),
        )); 

        return $this;

  }

}

Answer 1

You will need to add a column to the admin_user table.

$installer->getConnection()->addColumn($installer->getTable('admin/user'), 'ldap_user', array(
    'type' => Varien_Db_Ddl_Table::TYPE_TEXT,
    'length' => 256,
    'nullable' => true,
    'default' => null,
    'comment' => 'Ldap user'
)); 

Then, if you want to add/edit this field from the backend you need to rewrite the method Mage_Adminhtml_Block_Permissions_User_Edit_Tab_Main::_prepareForm and add a new element in there:

        $fieldset->addField('ldap_user', 'select', array(
            'name'      => 'is_active',
            'label'     => Mage::helper('adminhtml')->__('LDAP user'),
            'id'        => 'is_active',
            'title'     => Mage::helper('adminhtml')->__('LDAP user'),
            'class'     => 'input-select',
            'style'     => 'width: 80px',
            'options'   => array('1' => Mage::helper('adminhtml')->__('Yes'), '0' => Mage::helper('adminhtml')->__('No')),
        )); 

Clear the cache and it should work.