Mobile App webframe Authentication with Rails Devise

I am currently working on implementing a mobile app for our site that uses Ruby on Rails and Devise. The idea here is, at first, create a mobile login form that on successful login opens a web frame that is authenticated and allows the normal use of the (mobile optimised) site. Theoretically that should be possible. I am having trouble with the following issues:

1. How do you get the pure session key for the user session via a json request? What methods can be used to manually generate it from devise, something that the sign_in(:user, user) method does?

2. Is it even possible to take that key and put it into the browser cookie the way it normally happens in devise, but on the mobile side?

I know that this is not the standard method of making mobile applications for the site, but I believe it should be possible.