User rails console to login as a specific user

I'm using the rails console to and app.get to try to track down a bug that only happens for a specific user. Is there a way to issue a request as that user with apt.get?

Also, I don't have the user's password.

app.get '/account/billing'

Returns a 302 that is redirecting me to the login page. I do have a cookie from an actual request, so one idea I had was to try to stick that in the header so the request would look like it came from that user.

I'm using Rails 3.2.0 for this.