Can chrome.identity.launchWebAuthFlow be used to authenticate against Google APIs?

Yes, in 2019 it still works. Finally got it working...

manifest.json

{
   "name": "Extension Name",
   "description": "Description",
   "version": "1.0.0",
   "manifest_version": 2,
   "icons": {
      "48": "icons/icon_48.png",
      "128": "icons/icon_128.png"
   },
   "background": {
      "scripts": [
         "background.js"
      ],
      "persistent": false
   },
   "oauth2": {
      "client_id": "Your Client ID from Google Develpers console (Must be Web Application)",
      "scopes": [
         "openid", "email", "profile"
      ]
   },
   "permissions": [
      "identity"
   ],
   "key": "Your Key from Google Developer Dashboard"
}

background.js

chrome.windows.create({
    'url': './content/auth/auth.html',
    'width': 454,
    'height': 540,
    'type': 'popup'
});

auth.html

standard HTML markup that calls auth.js file

auth.js

var auth_url = 'https://accounts.google.com/o/oauth2/auth?';
var client_id = '<Client ID>';  // must be Web Application type
var redirect_url = chrome.identity.getRedirectURL(); // make sure to define Authorised redirect URIs in the Google Console such as https://<-your-extension-ID->.chromiumapp.org/

var auth_params = {
    client_id: client_id,
    redirect_uri: redirect_url,
    response_type: 'token',
    scope: 'https://mail.google.com/',
    login_hint: '[email protected]' // fake or non-existent won't work
};

const url = new URLSearchParams(Object.entries(auth_params));
url.toString();
auth_url += url;

chrome.identity.launchWebAuthFlow({url: auth_url, interactive: true}, function(responseUrl) { 
    console.log(responseUrl);
});

To get the Angular sample running, I needed to:

1. Create my own Web Application client ID in the Google developer console with an Authorized redirect URI of https://bcgajjfnjjgadphgiodlifoaclnemcbk.chromiumapp.org/oauth2

2. Copy that client ID into the config.json file of the sample.

The call to get redirectURI in that sample is like chrome.identity.getRedirectURL("oauth2"), the string parameter gets appended to the end of the URL based on extension ID.