session.js

import Ember from 'ember';

const slice = Array.prototype.slice;

const computedPromise = function() {
  const fn = slice.apply(arguments, [arguments.length-1, arguments.length])[0];
  const dependentKeys = slice.apply(arguments, [0, arguments.length-1]);

  return Ember.computed(...dependentKeys, function() {
    const PromisableObjectProxy = Ember.ObjectProxy.extend(Ember.PromiseProxyMixin);
    const promise = fn.apply(this);

    return PromisableObjectProxy.create({
      promise: Ember.RSVP.resolve(promise)
    });
  });
};

export default Ember.Service.extend({
  store: Ember.inject.service('store:main'),
  token: Ember.computed(function() {
    return 'secret';
  }),
  currentUser: computedPromise('token', function(){
    return this.get('store').find('user', { token: this.get('token') }).then(function(users) {
      return users.get('firstObject');
    });
  })
});