Captcha Plugin

This part describes how to develop a Captcha plugin.

The Captcha plugin works like following: The plugin register a Captcha provider, on onCaptchaSetup event, then system will use it depend on what is selected in the global configuration and how the Captcha field is configured in the form.

Events in this group:

onCaptchaSetup

onCaptchaSetup

Event signature:

function onCaptchaSetup(Joomla\CMS\Event\Captcha\CaptchaSetupEvent $event){}

Event attributes:

/** 
 * @var Joomla\CMS\Captcha\CaptchaRegistry $subject 
 */
$subject = $event->getCaptchaRegistry();

Creating a captcha plugin

The captcha plugin consist with two main things:

• The Captcha provider class, which provide a captcha logic for rendering input and for validation.
• The Plugin in Captcha group, which register the provider, so system know it existence.

Following example assume you already know how to create Joomla plugin.

Let's create a simple Honeypot captcha.

For start create a plugin under plugins/captcha/honeypot/ folder, call it honeypot, assume namespace is JoomlaExample\Plugin\Captcha\Honeypot.

Then create a Honeypot captcha provider, which will live under plugins/captcha/honeypot/src/Provider/HoneypotCaptchaProvider.php.

namespace JoomlaExample\Plugin\Captcha\Honeypot\Provider;

use Joomla\CMS\Captcha\CaptchaProviderInterface;
use Joomla\CMS\Form\FormField;

/**
 * Provider for Honeypot Captcha
 */
final class HoneypotCaptchaProvider implements CaptchaProviderInterface
{
    /**
     * Return Captcha name, CMD string.
     *
     * @return string
     */
    public function getName(): string
    {
        return 'honeypot';
    }
    
    /**
     * Render the captcha input
     *
     * @param   string  $name        Input name given in the form
     * @param   array   $attributes  The class of the field and other attributes, from the form.
     *
     * @return  string  The HTML to be embedded in the form
     *
     * @throws  \RuntimeException
     */
    public function display(string $name = '', array $attributes = []): string
    {
        return '<input type="hidden" value="" name="' . $name . '" id="' . ($attributes['id'] ?? '') . '" class="' . ($attributes['class'] ?? '') . '"/>';
    }
    
    /**
     * Validate the input data
     *
     * @param   string  $code  Answer provided by user
     *
     * @return  bool    If the answer is correct, false otherwise
     *
     * @throws  \RuntimeException
     */
    public function checkAnswer(string $code = null): bool
    {
        return !$code;
    }
    
    /**
     * Method to react on the setup of a captcha field. Gives the possibility
     * to change the field and/or the XML element for the field.
     *
     * @param   FormField         $field    Captcha field instance
     * @param   \SimpleXMLElement  $element  XML form definition
     *
     * @return void
     *
     * @throws  \RuntimeException
     */
    public function setupField(FormField $field, \SimpleXMLElement $element): void
    {
        // Hide the label for this captcha type
        $element['hiddenLabel'] = 'true';
    }
}

Register the provider in the system with a plugin and event:

namespace JoomlaExample\Plugin\Captcha\Honeypot\Extension;

use Joomla\CMS\Plugin\CMSPlugin;
use Joomla\Event\SubscriberInterface;
use JoomlaExample\Plugin\Captcha\Honeypot\Provider\HoneypotCaptchaProvider;

final class HoneypotCaptcha extends CMSPlugin implements SubscriberInterface
{
    /**
     * Returns an array of events this plugin will listen to.
     *
     * @return  array
     */
    public static function getSubscribedEvents(): array
    {
        return [
            'onCaptchaSetup' => 'onCaptchaSetup',
        ];
    }
    
    /**
     * Register Captcha instance
     *
     * @param CaptchaSetupEvent $event
     *
     * @return void
     */
    public function onCaptchaSetup(CaptchaSetupEvent $event)
    {
       $event->getCaptchaRegistry()->add(new HoneypotCaptchaProvider());
    }
}

And all done 🎉 After plugin installation and enabling this new captcha will be available in Global configuration to use.