// Utility function to link a user's twitter info to the current user.
function _linkIdentity() {
    var identityOptions = {
            id: this.params.raw.user_id,
            accessToken: this.params.access_token,
            accessSecret: this.params.access_secret,
            screen_name: this.params.raw.screen_name
        };

    return BB.resolve(grasshopper.request(this.token).users.linkIdentity(this.user._id.toString(), 'twitter', identityOptions));
}
 .then(function() {
     return grasshopper.request(this.token).users.current();
 })