Add access to authentication state via context

[thekid]

Implements #7 by using a request value named context.

Update user

Before:

return [
  '/theme' => $auth->required(function($req, $res) use($sessions) {
    if ($session= $sessions->locate($req)) {
      [$claims, $user]= $session->value('auth');
      $user['theme']= $req->params('theme');
      $session->register('auth', [$claims, $user]);
      $session->transmit($res);
    }

    $res->answer(202);
  }),
  // ...
];

After:

return [
  '/theme' => $auth->required(function($req, $res) {
    $req->value('context')->modify(['theme' => $req->param('theme')]);
    $res->answer(202);
  }),
  // ...
];

Logout

Before:

return [
  '/logout' => $auth->required(function($req, $res) use($sessions) {
    if ($session= $sessions->locate($req)) {
      $session->destroy();
      $session->transmit($res);
    }

    $res->answer(302);
    $res->header('Location', '/?logged-out');
  }),
  // ...
];

After:

return [
  '/logout' => $auth->required(function($req, $res) {
    $req->value('context')->logout();
    $res->answer(302);
    $res->header('Location', '/?logged-out');
  }),
  // ...
];

[thekid]

Should we be able to register (cache) arbitrary values in the session?

$context= $req->value('context');

// Explicit read/write
$cities= $context->value('cities');
$context->register('cities', $cities);

// Access cache, fetch from repository if necessary
$cities= $context->cache('cities', $repository->cities(...));

// After <TTL> seconds, refresh from repository
$cities= $context->cache('cities', $repository->cities(...), ttl: 3600);