code: function (req, res, next) {
      var prifile = req.profile;
      var filter = { or: [{ twitter: profile.user_id }, { email: profile.email }] };
  
      User.find({ where: filter }, function(err, users) {
        var user = users[0];
  
        if (user) {
          if (!user.twitter) {
            user.twitter = profile.user_id;
            user.displayName = user.displayName || profile.name;
            user.save(function() {
              req.user = user;
              next();
            });
            return;
          }
  
          req.user = user;
          next();
          return;
        }
  
        User.create({
          displayName: profile.name,
          yahoo: profile.user_id,
          email: profile.email,
          password: profile.user_id
        }, function (err, user) {
          req.user = user;
          next();
        });
  
      });
    }
docs: Step 4b. Create a new user account or return an existing one.