The session disappears quickly

I have a question about the session of cakephp.

On one page

$session=$this->getRequest()->getSession();
$session->write('username', 'test');

and on another page.

$session=$this->getRequest()->getSession();
$username=$session->read('username');
var_dump($username);

However, it will be null.

Is there something you haven't set up yet?

The version is
cakephp3.7.4
That's it.

Thank you for your cooperation.