How to Override the Default Universe Domain

 google::cloud::Options options;
 // AddUniverseDomainOption interrogates the UnifiedCredentialsOption, if set,
 // in the provided Options for the Universe Domain associated with the
 // credentials and adds it to the set of Options.
 // If no UnifiedCredentialsOption is set, GoogleDefaultCredentials are used.
 auto ud_options = google::cloud::AddUniverseDomainOption(std::move(options));
 if (!ud_options.ok()) throw std::move(ud_options).status();
 auto ud_client = google::cloud::appengine_v1::ApplicationsClient(
 google::cloud::appengine_v1::MakeApplicationsConnection(*ud_options));