[Ask] Using Session For Accessing Yii

Hi, everyone. I wanna ask about the Session ($_SESSION) function in yii. Let say that I have one yii’s application, which i use username and password to get into this. In another way, there’s another web application, which has a main database of staff identity (include username and password). my question is, how could I login into my yii’s while I type both the username’s and password’s main data/staff identity? there’s a way that I know, is using Session for getting data, but i really didn’t know the exact step… Thanks in advance… :D