Multiple vue.js app instance support

[Andrei-Pozolotin]

1. this approach:
   https://d0whc3r.github.io/vue-auth-plugin/installation.html#use-vue-router-and-vuex

const store = new Vuex.Store({ ... });
(Vue as any).store = store;

      if (!_this.Vue.store) {
526:        throw Error('[vue-auth-plugin] vuex is a required dependency if you want to use "vuex" as storage');
      }

vue-auth-plugin.umd.js:526 Uncaught Error: [vue-auth-plugin] vuex is a required dependency if you want to use "vuex" as storage
    at new StoreVuex (vue-auth-plugin.umd.js:526)
    at vue-auth-plugin.umd.js:650
    at Array.map (<anonymous>)
    at AuthStoreManager.setStores (vue-auth-plugin.umd.js:640)
    at new AuthStoreManager (vue-auth-plugin.umd.js:622)
    at new Auth (vue-auth-plugin.umd.js:1833)
    at Object.install (vue-auth-plugin.umd.js:1893)
    at Function.Vue.use (vue.js:5094)
    at vue-auth-plugin.umd.js:1910
    at vue-auth-plugin.umd.js:9

2. prevents using multiple vue.js app instances:
   https://vuex.vuejs.org/guide/state.html
   when store is injected per-instance:

const app = new Vue({
  el: '#app',
  // provide the store using the "store" option.
  // this will inject the store instance to all child components.
  store,
  components: { Counter },
  template: `
    <div class="app">
      <counter></counter>
    </div>
  `
})

3. instead, VueAuthPlugin should behave as store-attached plugin:
   https://vuex.vuejs.org/guide/plugins.html

const store = new Vuex.Store({
  // ...
  plugins: [VueAuthPlugin] // can be class or instance
})

[d0whc3r]

If you have a solution for this, could you make a pr?

[Andrei-Pozolotin]

a solution could be a change to a lazy-init pattern:

  Object.defineProperties(Vue.prototype, {
    $auth: {
      get: function get() {
        if (!this.__auth__) {
          if (this.$http) { /* use user-provided axios */ } else { /* use default http provider */ }
          if (this.$store) { /* use user-provided vuex */ } else { /* ... */ }
          if (this.$router) { /* use user-provided vue-router */ } else { /* ... */ }
          this.__auth__ = new VueAuthCore(this.$http, this.$store, this.$router, options);
        }
        return this.__auth__
      }
    }
  });