OpenCart with symfony

Hy guys,
I developed a symfony application 2 years ago. Now I need to integrate a shop to this project and I choose Opencart. I can share the database and adapt my old application but my problem is that I don't know how to share session. I ony want to login once (in the old application or in the opencart). Do you know how could I do it? Any suggestion?
Thanks in advance,
Cristina