Implement isallowed twig function

src/Twig/UserExtension.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Bolt\Twig;
+
+use Symfony\Component\Security\Core\Security;
+use Twig\Extension\AbstractExtension;
+use Twig\TwigFunction;
+
+class UserExtension extends AbstractExtension
+{
+    /** @var Security */
+    private $security;
+
+    public function __construct(Security $security)
+    {
+        $this->security = $security;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getFunctions(): array
+    {
+        return [
+            new TwigFunction('isallowed', [$this, 'isAllowed']),
+        ];
+    }
+
+    /**
+     * @todo Replace with better method, once we've implemented https://github.com/bolt/core/issues/186
+     */
+    public function isAllowed(): bool
+    {
+        if ($this->security->getUser()) {
+            return true;
+        }
+
+        return false;
+    }
+}