Provide a way to create AuthCredentials given an AccessToken

[aozarov]

GoogleCredentials supports creating an instance using a temporary AccessToken.

It would be nice to support it.

We could do that by getting the token string and expiration time and adding ourselves as AuthCredentials.CredentialsChangedListener to capture token updates.

[garrettjonesgoogle]

Some analysis would need to be done to see if this is still relevant.

[danoscarmike]

This issue may no longer be relevant due to its age. If you are still experiencing this issue and are reasonably certain that it is a bug, please feel free to re-open this it with enough information to help us reproduce it.