code: @Beta
    public GoogleCredential createDelegated(String user) {
      if (serviceAccountPrivateKey == null) {
        return this;
      }
      return toBuilder()
          .setServiceAccountUser(user)
          .build();
    }
docs: {@link Beta} <br/>
  For service accounts that need to delegate to a specific user, create a
  copy of the credential with the specified user.