Retrieving google photos with IONIC 3 with google photos API

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 scope

Here is the code:

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

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