How to manually create a new session in symfony 1.4 - php

Question

I am working on a symfony project which is made of 2 applications (frontend & backend) and I have been asked to manually create a second session in the backend so that the administrator could access user data (the frontend) from the backend without logging in.
I've set different names in factory.yml so that each application has its own cookie.
Basicalyy, I need to retrieve a user from the backend, manually create the frontend cookie without destroying the backend session then redirect to the frontend.
I've tried the following code but this doesn't work :
$user = $this->getUser()->getAttribute('some_attribute');
$session = new sfSessionStorage();
$option = array(
'session_name' => 'frontend_session_name'
);
$session->initialize($options);
// some code to push the user in the new cookie
$this->redirect('https://frontend.php');
I haven't been using symfony for long and must admit that I'm a bit lost here. I know I need to populate the new cookie with the user data but I can't figure out how.
Any help will be very much appreciated.
edit: I forgot to mention that I'm using propel.
edit #2: I've come up with the following solution which does what intended :
$user = $this->getUser()->getAttribute('some_attribute'); //retrieving the user whose data I'd like to access
$currentSessionId = session_id();
session_write_close();
session_name('frontend_session_name');
session_start();
session_regenerate_id();
$_SESSION['symfony/user/sfUser/culture'] = 'en';
$_SESSION['symfony/user/sfUser/lastRequest'] = time();
$_SESSION['symfony/user/sfUser/authenticated'] = 1;
$_SESSION['symfony/user/sfUser/credentials'] = array('frontend_user');
$_SESSION['symfony/user/sfUser/attributes'] = array(
'symfony/user/sfUser/attributes' => array(
'user' => $user
)
);
session_write_close();
session_name('backend_session_name');
session_id($currentSessionId);
session_start();
$this->redirect('/frontend.php');
So I just manually recreated the session and pushed in the necessary data.
Thanks to those who tried to help.

Answer 1

As sharing a session doesn't seem to be an option for you, I'd suggest:
creating a unique key for each user, not the id, but a separate string that is hard to guess
create a module / action on the frontend that accepts the key as a parameter, finds the corresponding user in the database, and logs them in
You could then generate the required links in the backend that an admin can click and be redirected to.
Not very secure, make sure your keys are long. You'd need to add code to prevent brute forcing, and limit access to the action by IP address maybe?
You could also require the key of the admin user, and check that it is valid too, which would make it harder to guess.