My custom authenticator

_config.php

<?php

global $project;
$project = 'mysite';

global $database;
$database = '';

require_once 'conf/ConfigureFromEnv.php';

// Set the site locale
i18n::set_locale('en_US');

// set up My authentication
Authenticator::register_authenticator('MyAuthenticator');
Authenticator::set_default_authenticator('MyAuthenticator');
Authenticator::unregister_authenticator('MemberAuthenticator');

MyAuthenticator.php

<?php

class MyAuthenticator extends MemberAuthenticator {

    /**
     * Attempt to find and authenticate member if possible from the given data
     *
     * @param array $data
     * @param Form $form
     * @param bool &$success Success flag
     * @return Member Found member, regardless of successful login
     */
    protected static function authenticate_member($data, $form, &$success)
    {
        // clearly this is not clever because all the success/failure hooks get called regardless of my custom logic
        $member = parent::authenticate_member($data, $form, $success);

        // randomly fail one in 3 logins
        if ($success && rand(1,3) == 1) {
            $success = false;
            $form->sessionMessage('Today was not your lucky day', 'bad');
        }

        if ($success) {
            return $member;
        }
    }

    public static function get_login_form(Controller $controller) {
        return MyLoginForm::create($controller, "LoginForm");
    }

}

MyLoginForm.php

<?php

class MyLoginForm extends MemberLoginForm {

    protected $authenticator_class = 'MyAuthenticator';

}