Select Google OAuth2 API v2 for Scope

On the dashboard you will be on Step 1: Select & authorize APIs, from the menu select Google OAuth2 API v2 dropdown for Scope.

Select email scope and Authorize API's

Select the https://www.googleapis.com/auth/userinfo.email scope and click on Authorize APIs button.

Login with your Google Account

Select the google account for which you want to generate the token and click on Continue button.

Exchange authorization code for tokens

You will be redirected to Step 2: Exchange authorization code for tokens page where you can click Exchange authorization code for tokens button.

Copy the token

Under the Request / Response tab, you will get the token_id. Copy the token and use it in the authenticate request.