[1157] Check logged user in firebase with middleware

I've built some auth middleware:

import api from '~/api/Api.js'

export default function ({router, store}) {
  return api.auth().onAuthStateChanged(function (user) {
    store.state.user = user
    if (user) {

    } else {

    }
  })
}

Now, how to actually get access to the user object? When i'm doing this from normal component it's working correctly. Passing to store simple string also works, but any other action no, is there need of some kind of promise? Thx for help.