Saving mongoose result in a variable outside a callback

Question

I am trying to return found entry from a Mongoose entry on my collection into a variable which the function will return after few more checks.

The current code is getting the document, but I need to access it and return it at the end. Is it possible to assign a return query outside the callback?

The current function:

login_user(username, psw) {
        let hashedPsw = _SECURITY.string_to_sha1(psw);
        let userObject = {};
        webkbuser.findOne({'user_username': username}).exec(function(err, ret) {
            if (err) return _UTILS.errorHanlder(err, false, true, null);
            userObject = ret;
        });
        console.log(userObject);
}

As predicted the console.log returns a '{}' output since nothing is getting assigned to it.

The object is being created in a router and login is being called in if statement atm

    router.post('/', function(req, res, next) {
      if (!req.body) return res.sendStatu(400);
      if (!req.body.usr) return res.sendStatus(400);
      if (!req.body.psw) return res.sendStatus(400);
      let user = new _USER('LOGIN');
      if (user.login(req.body.usr, req.body.psw) === false) return res.sendStatus(401);
      req.session.active = true;
      res.sendStatus(200);
    })