Moodle web login from app

Hi, 

I'm trying to build an app that use my Moodle content. I use the Moodle 

external service to get the courses list. I want to show the courses content 

by opening my Moodle site at the right page. The user is already login with 

his credentials in the app. Is it a way to login the Moodle site before loading 

the course site?

Thanks