Google Calendar API Not Receiving the Refresh token

Question

I'm using Google Calendar API in my application.when I'm Authenticating user I'm getting one issue . ie, one user is logged into gmail in one tab.who has already access to the application.now I Opened the application in other tab and trying to make request to authenticate. it is not asking any account details.directly it is redirecting into application.i Don't know why ? how to resolve this can please tell me.