Sync method + session

help
1

im trying to sync a Session.set at Meteor.call() AFTER getting userID from Mongo

severside:

RegisterLayout: function(username, fullname, password){
Users.insert({
username: username,
fullname: fullname,
password: password,
tickets: 3,
currency: 200
});

var userFound = Users.findOne({
username: username
});

 var data = userFound._id;
 console.log(data);
return data;
}

Client Code:

Meteor.call('RegisterLayout', regUserName, regFullName, regPassword, function(error, data){
  if(error){
    console.log(error);
  } else {
  FlowRouter.go('/main');
  Session.setAuth("loggedIn", data);

The result is: user being logged in but session is set to undifined because the server doesn’t responds synchronously. Is there a way to “Stop/Block” the code from executing untill the server will get a response from mongo with the usersID so I can set session?