Wordpress MU User Integration

Hello everyone.

Does anyone have an idea how could I integrate User table from Wordpress MU with Opencart?
I would like to provide single sign on possibility, so users does not have to register twice.
Is it somehow possible to get Opencart to accept Wodpress User Table, or the way around?

An other idea was to use some sort of synchronization of both user tables, or to use for ex. open ID for singing in?

I am new to Opencart and don´t know where to start? Maybe someone had to solve a similar situation.

Thank you all!

Has anyone done this?