同一会话，不同的域，设置会话ID

I have a couple of domains which i want to shere sessions. I have created a method like this:

The user login is done in a central place and the sessions are saved in the database.

Lets say the user A wants to go to abc.com domain. My app redirects it to the main authentication domain where he logs in. After login is generated an auth token which is saved in a field in the sessions table and it is pass back to the abc.com application.

There I use the auth_token to get the session_id from the database and to set the session_id of abc.com the same.

The problem is that it allways creates a new session.

This is my code of the abc.com

$sessionId = // get from the database using the auth_token.
 /* CLOSE PREVIOUS SESSION */
            session_destroy();

// sets the new id.  
            session_id($sessionId);

            /** start new session * */
            session_start();

What i am missing?. I am using php with Symfony framework. Dont know if it´s related with symfony session handling.

Ok. I solved my problem. I had to delete the old session cookie after calling session_destroy().

Here is my full code if someone is interested:

$sessionId =  // get session id from  the database using the auth_token
session_destroy();

$this->getResponse()->setCookie('mycookie',null,time()-3600);

session_id($sessionId);

/** start new session * */

session_start();

$this->getResponse()->setCookie('mycookie', $sessionId,null,null,'mydomain');

Thanks everyone for the help.