Ghost/ghost/admin/app/controllers/application.js

import Controller from '@ember/controller';
import {computed} from '@ember/object';
import {inject as service} from '@ember/service';

export default Controller.extend({
    dropdown: service(),
    session: service(),
    settings: service(),
    ui: service(),

    showNavMenu: computed('currentPath', 'session.{isAuthenticated,user.isFulfilled}', function () {
        // we need to defer showing the navigation menu until the session.user
        // promise has fulfilled so that gh-user-can-admin has the correct data
        if (!this.get('session.isAuthenticated') || !this.get('session.user.isFulfilled')) {
            return false;
        }

        return (this.get('currentPath') !== 'error404' || this.get('session.isAuthenticated'))
                && !this.get('currentPath').match(/(signin|signup|setup|reset)/);
    })
});