title: How to get Bearer access token for a user account to access protected data in cloud storage bucket
body: <p>I am trying to build a web application where a user log's in and access protected data in cloud storage bucket (firebase authentication used for login). ACL is set for objects in cloud storage. The user should be able to read only the objects that he has access to.
  I want to get Bearer access token for the user, the access token should have his scopes, when I send a REST request with the bearer token, I should be able to read the objects in bucket for which he has access to, if the user don't have access, I should get access denied message. I cant use service account here as I am getting data specific to a user.
  How can I do this, suggestions please and Thanks in advance.</p>