Check for ID token in OAuth token if access token is not set.
Check for ID token in OAuth token if access token is not set.

Some Google services, for example GCP IAP, don't set access token but set id_token in the OAuth token JSON. Use id_token if that's the case.

PiperOrigin-RevId: 335465851

google/cloudprober,cloudprober/cloudprober,google/cloudprober,cloudprober/cloudprober,cloudprober/cloudprober