There are a few related issues about migrating from deprecated GoogleCredential to GoogleCredentials
e.g. #1103
#1386
googleapis/google-cloud-java#12608

We need some guide around achieve similar functionality with GoogleCredentials.
Perhaps linking to https://developers.google.com/api-client-library/java/google-api-java-client/requests from README