Form.php

<?php

namespace My\Modules\Authentication\Form;

use Zend\Form\Form;
use Zend\InputFilter\InputFilterProviderInterface;

class ChangePassword extends Form implements InputFilterProviderInterface
{
    public function __construct()
    {
        parent::__construct('change-password');
    }

    public function init()
    {
        $this->add(array(
            'type' => 'Zend\Form\Element\Password',
            'name' => 'old-password',
            'options' => array(
                'label' => 'Old Password',
            ),
        ));

        $this->add(array(
            'type' => 'Zend\Form\Element\Password',
            'name' => 'new-password',
            'options' => array(
                'label' => 'New Password',
            ),
        ));

        $this->add(array(
            'type' => 'Zend\Form\Element\Password',
            'name' => 'new-password-confirm',
            'options' => array(
                'label' => 'New Password (confirm)',
            ),
        ));

        $this->add(array(
            'type' => 'Zend\Form\Element\Csrf',
            'name' => 'csrf',
        ));

        $this->add(array(
            'type' => 'Zend\Form\Element\Button',
            'name' => 'submit',
            'options' => array(
                'label' => 'Change',
            ),
            'attributes' => array(
                'type' => 'submit',
            ),
        ));
    }

    public function getInputFilterSpecification()
    {
        return array(
            'old-password' => array(
                'filters'  => array(
                    array('name' => 'Zend\Filter\StringTrim'),
                ),
            ),
            'new-password' => array(
                'filters'  => array(
                    array('name' => 'Zend\Filter\StringTrim'),
                ),
                'validators' => array(
                    array(
                        'name' => 'Zend\Validator\StringLength',
                        'options' => array(
                            'min' => 5,
                            'max' => 63,
                        ),
                    ),
                ),
            ),
            'new-password-confirm' => array(
                'filters'  => array(
                    array('name' => 'Zend\Filter\StringTrim'),
                ),
                'validators' => array(
                    array(
                        'name' => 'My\Validator\Confirm',
                        'options' => array(
                            'field' => 'new-password',
                        ),
                    ),
                ),
            ),
        );
    }
}

Validator.php

<?php

namespace My\Validator;

use Zend\Validator\AbstractValidator;

class Confirm extends AbstractValidator
{
    const DIFFERENT_FROM = 'DIFFERENT_FROM';

    protected $messageTemplates = array(
        self::DIFFERENT_FROM => 'Value differs from original one',
    );

    private $field;

    public function __construct(array $options = array())
    {
        if (! isset($options['field'])) {
            throw new Exception\InvalidArgumentException('Field to check missing');
        }

        $this->field = $options['field'];

        parent::__construct($options);
    }

    public function isValid($value, $context = null)
    {
        if (! is_array($context) or ! isset($context[$this->field])) {
            throw new Exception\RuntimeException(sprintf('Field "%s" missing in the context', $this->field));
        }

        $this->setValue($value);

        if ($value !== $context[$this->field]) {
            $this->error(self::DIFFERENT_FROM);

            return false;
        }

        return true;
    }
}