tos/Form/AcceptTosType.php

<?php
namespace vierbergenlars\AuthserverTosBundle\Form;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\Extension\Core\Type\CheckboxType;
use Symfony\Component\Validator\Constraints\IsTrue;

class AcceptTosType extends AbstractType
{

    private static function generateTermLink(array $term)
    {
        return 'the <a href="' . htmlentities($term['url'], ENT_HTML5 | ENT_QUOTES) . '">' . htmlentities($term['label'], ENT_HTML5) . '</a>';
    }

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $terms = $options['terms'];
        if (count($terms) > 1) {
            $lastItem = ' and ' . self::generateTermLink(array_pop($terms));
        } else {
            $lastItem = '';
        }
        $termsString = implode(', ', array_map([
            self::class,
            'generateTermLink'
        ], $terms)) . $lastItem;

        $builder->add('accept', CheckboxType::class, [
            'label' => 'I accept ' . $termsString,
            'attr' => [
                'align_with_widget' => true
            ],
            'constraints' => [
                new IsTrue([
                    'message' => 'You must accept.'
                ])
            ]
        ]);
    }

    /**
     *
     * {@inheritdoc}
     * @see \Symfony\Component\Form\AbstractType::configureOptions()
     */
    public function configureOptions(\Symfony\Component\OptionsResolver\OptionsResolver $resolver)
    {
        $resolver->setDefined('terms')
            ->setRequired('terms')
            ->addAllowedTypes('terms', 'array')
            ->setDefault('label', false);
    }
}