How to find the lifetime of a login token.

[rgelb]

I want to add a huge amount of photos (let's say 1000) which will takes a long time. After a while I get Request had invalid authentication credentials. Expected OAuth 2 access token, login cookie or other valid authentication credential error when calling any method on the library.

How do I find out when the OAuth access token is expiring?

P.S. My current workaround is to basically new up GooglePhotosService. Is there a better way?