Forum: Ruby on Rails facebook multiple signin problem

Hi
   I am working with ruby on rails application.
   I can make a user to signin facebook when he click the facebook 
button.
        I am having a button as Add facebook button, in that, when the 
user
click the button, he need to add one more facebook account.
        Since a user is already logged in, i cant able to show the 
facebook
signin page, it again logging with the same account.

Help me to solve this,
    I thought of logout the previous account, and make signin for the 
new
user.... but for logout we need previous user access token.. how can we 
get
who is logged in presently in our system.....  Is there a query to find 
a
person who is logged in presently in facebook

Thankx