title: Authentication session is not defined
body: <p>I try to use Google Photos API to upload my images, base on the steps of the following link.</p>
  
  <p><a href="https://developers.google.com/photos/library/guides/upload-media" rel="noreferrer">https://developers.google.com/photos/library/guides/upload-media</a></p>
  
  <p>After following the <a href="https://developers.google.com/identity/protocols/OAuth2WebServer" rel="noreferrer">Using OAuth 2.0 for Web Server Applications</a>, I just get the Oauth2.0_token response(a JSON format with access_token, refresh_token...). However, after I put this token string with "Bearer " into request headers, the response is error 401, the error message is "code 16 Authentication session is not defined". </p>
  
  <p>I cannot find any information to deal with it, thank for any help.</p>