There is a problem with credentials documentation [1]. It points at oauth 2.0 [2] which refers to GoogleCredential [3]. And that is listed as Deprecated.

Please somebody update to a non-deprecated example.

[1] https://developers.google.com/api-client-library/java/google-api-java-client/dev-guide
[2] https://developers.google.com/api-client-library/java/google-api-java-client/oauth2
[3] https://googleapis.dev/java/google-api-client/latest/com/google/api/client/googleapis/auth/oauth2/GoogleCredential.html