Hitting the url http://twitter.com/home?status=<status_msg> takes us to the twitter login page and once logged in, the status is already filled in the input box, ready to be tweeted.
Is there a similar url for following somebody on twitter ?
something of the form http://twitter.com/follow?user=<user_to be_followed> so that when this url is hit, the user is taken to login page(if not authenticated), and after a successfull login, the logged in user becomes a follower of the user in the url.
You could use OAuth. That will direct the user to Twitter for authentication and to authorize your app to act on their behalf. It will then give you a token that you can use to make API calls for that user.
It's not a terribly simple thing to implement and might be more trouble than it's worth for your situation, but the option is there. Look for a library for your platform of choice, they exist for most languages.