// The process
1. User provides details
2. Cake checks the database
3. If OK, then check the custom object method
4. If OK, return true

// What I'd like:
1. User provides details.
2. Check the custom object method
3. If OK, return true
4. Profit.

// app/controllers/components/ldap_auth.php
<?php
App::import('Component', 'Auth');
class LdapAuthComponent extends AuthComponent {
/**
 * Don't hash passwords
 */
    function hashPasswords($data){
        return $data;
    }
/**
 * We will initially identify the user
 */
    function identify($user=null, $conditions=null) {
        // bind credentials against ldap
        $ldapUser = $this->_ldapAuth($user); // do your stuff
        if (!$ldapUser) {
            return null; // if bind fails, then return null (as stated in api)
        }
        // get the cake model you would normally be authenticating against
        $model =& $this->getModel(); // default is User
        // check for existing User in mysql
        $user = $model->find('first', array('conditions' => array(
            'username' => $ldapUser['cn']
        ));
        // if no existing User, create a new User
        if (!$user) {
            $user = $model->save(array('User' => array(
                'username' => $ldapUser['cn'],
                // .. map needed ldap fields to mysql fields ..
            )));
            if (!$user) {
                $this->cakeError('ldapCreateUser');
            }
            // pass the id of the newly created User to Auth's identify
            return parent::identify($model->id, $conditions);
        }
        // pass the id of the existing User to Auth's identify
        return parent::identify($user[$this->userModel][$model->primaryKey], $conditions);
    }
/**
 * Lets check LDAP
 *
 * @return mixed Array of user data from ldap, or false if bind fails
 */
    function _ldapAuth($user) {
        $username = $user[$this->userModel][$this->fields['username']];
        $password = $user[$this->userModel][$this->fields['password']];
        // use the php ldap functions here
        return $ldapUser;
    }
}
?>

function hashPasswords($data) {
    $data['User']['password'] = 'a';
    return $data;
}

$this->Auth->authenticate = ClassRegistry::init('User');

// The process
1. User provides details
2. Cake checks the database **and always returns OK**
3. If OK, then check the custom object method
4. If OK, return true