The session will have the form key, no need to inject it into the template.

app/src/Handler/Channel/Page/CreateChannelPage.php

@@ -8,13 +8,8 @@ use Slovocast\Handler\Handler;
 
 class CreateChannelPage extends Handler
 {
-    public function __construct(
-        private SessionInterface $session
-    ) { }
-
     public function handle(): Response
     {
-        $formKey = $this->session->get("form_key");
         return $this->render('channel/create.twig', [ 'form_key' => $formKey ]);
     }
 }

app/src/Handler/User/Page/LoginUserPage.php

@@ -8,13 +8,8 @@ use Slovocast\Handler\Handler;
 
 class LoginUserPage extends Handler
 {
-    public function __construct(
-        private SessionInterface $session
-    ) { }
-
     public function handle(): Response
     {
-        $formKey = $this->session->get("form_key");
         return $this->render('user/login.twig');
     }
 }

app/src/Handler/User/Page/RegisterUserPage.php

@@ -8,13 +8,8 @@ use Slovocast\Handler\Handler;
 
 class RegisterUserPage extends Handler
 {
-    public function __construct(
-        private SessionInterface $session
-    ) { }
-
     public function handle(): Response
     {
-        $formKey = $this->session->get("form_key");
         return $this->render('user/register.twig', [ 'form_key' => $formKey ]);
     }
 }

app/templates/user/login.twig

@@ -3,6 +3,7 @@
 {% block content %}
 <div>
     <form action="/login" method="post">
+        <input name="form_key" type="hidden" value="{{ session.get('form_key') }}"
         <div>
             <label for="email">Email<br>
             <input name="email" type="text" required>