title: Change credentials on GCloud API Storage manually due to account used is deleted
body: <p>i would like to ask.
  There is a Golang instance running, which has features to upload/download to Google Cloud Storage API. Due to last developer is out and the credentials used is his, now his account is deleted.
  Can i change the credentials manually to my account?</p>
  
  <p>Sorry for bad explanation but i will try to give more details if u guys asked.</p>
  
  <p>This is the response which i get if i access Google Cloud Storage API.</p>
  
  <pre><code>message: "Post https://www.googleapis.com/upload/storage/v1/b/psb/o?alt=json&amp;projection=full&amp;uploadType=multipart: oauth2: cannot fetch token: 400 Bad Request↵Response: {↵  "error": "invalid_grant",↵  "error_description": "Account has been deleted"↵}"
  </code></pre>
  
  <p>status: "500 Internal Server Error"</p>