"this" is undefined in torii-adapter in ember

I am trying to store some data post login inside store. Below is code of my torii-adapter

import Ember from 'ember';
import {createToken} from 'myapp/utils/app-utils';

export default Ember.Object.extend({
  store: Ember.inject.service(),

  open: function(authentication){
    let authorizationCode = authentication.authorizationCode;
    let token = createToken();
    return new Ember.RSVP.Promise(function(resolve, reject){
      console.log(authentication);
      Ember.$.ajax({
        url: 'http://localhost/getUserInfoWuthAuthCode.php',
        data: { 'code': authorizationCode,token:token},
        success: Ember.run.bind(null, resolve),
        error: Ember.run.bind(null, reject)
      });
    }).then(function(data){
      let user = data.user[0];
      this.set('storage.token',token); //this is undefined
      return {
        user: user
      };
    });
  }

});

Error i am getting is "TypeError: Cannot read property 'set' of undefined". I am injecting the store service as well. Could you please tell me what exactly is going wrong here?

this is not defined in your current context. Assign it to another varible.

  open: function(authentication){
    let authorizationCode = authentication.authorizationCode;
    let token = createToken();
    let that = this;
    return new Ember.RSVP.Promise(function(resolve, reject){
      console.log(authentication);
      Ember.$.ajax({
        url: 'http://localhost/getUserInfoWuthAuthCode.php',
        data: { 'code': authorizationCode,token:token},
        success: Ember.run.bind(null, resolve),
        error: Ember.run.bind(null, reject)
      });
    }).then(function(data){
      let user = data.user[0];
      that.set('storage.token',token); //this is undefined
      return {
        user: user
      };
    });
  }

To get further understanding and to see different options (such as fat arrow or bind method), have a look at this question.