Someone should write a cron job that logs into your yahoo account once a month so it doesn't go inactive.

You'll probably want the logs mailed to you, or put somewhere you'll look at regularly, because Yahoo's login interface is probably a moving target and you want to know when you need to rewrite your script due to Yahoo's changes.

Or does Yahoo have stable, published API's you could use for this?

This should be open-source, there's no way I'm giving my Yahoo ID and password to some third-party product I can't inspect.