Rails: share sessions across subdomains?


I’m writing Rails applications on a DreamHost domain, and I have subdomains which also are using Rails. What I’m trying to provide a login page which will log the user in across all subdomains. Is this possible?

(It’s a lot like logging into Yahoo Mail at mail.yahoo.com and still having your session active on finance.yahoo.com so you don’t have to log in again.)

Thanks in advance!