Retrieving google photos with IONIC 3 with google photos API

Ionic Framework ionic-v3
1

I am working on an IONIC 3 application.
In this app the user will be able to get photos from his google photos account and do some design manipulations on the image he selected.

So for that I want to use the google photos API

I did not find any example on how to accomplish this in IONIC.

I tried to do it like this:

Login to google with: cordova-plugin-googleplus
And request the https://www.googleapis.com/auth/photoslibrary scope

Here is the code:

//Here we do a login.
this.gplus.login({
   'webClientId': '***********',
   'offline': true,
   'scopes': 'profile email https://www.googleapis.com/auth/photoslibrary'
}).then((res) => {
   //after login we try to get the google photos albums
   this.http.get('https://photoslibrary.googleapis.com/v1/albums', {
      responseType: ResponseContentType.Json,
      params:{
         accessToken: res.accessToken,
         pageSize: 50,          
      }
   }).subscribe(res=>{
      console.log('<--- google images res: ', res);
   },err=>{
      console.log('<--- google images err: ', err);
   });
});

Now I get an error ‘Expected OAuth 2 access token’
Here is the full error description:

Request is missing required authentication credential. 
Expected OAuth 2 access token, login cookie or other valid authentication credential. 
See https://developers.google.com/identity/sign-in/web/devconsole-project.

So now the question is how do is get an OAuth 2 access token ?