How to prevent automatic Signup with loginWithService


I’m using the default Meteor.loginWithService to sign users up with Twitter accounts. But by default Meteor.loginWithService signs up, or adds a user and logs them in if you call the method. Doesn’t matter if it’s called for users who don’t have accounts (eg. signed up with a unique token). How can I prevent this? Eg. almost a difference between Meteor.loginWithService and Meteor.signupWithService.