Emit an event when a specific piece of state changes in vuex store

Just set a getter for the authed state in your component and watch that local getter:

watch: {
  'authed': function () {
    ...
  }
}

Or you can use ...

let suscribe = store.subscribe((mutation, state) => {
  console.log(mutation.type)
  console.log(mutation.payload)
})
// call suscribe() for unsuscribe

https://vuex.vuejs.org/api/#subscribe