Unless otherwise configured, the client libraries use Application Default Credentials to authenticate with Google Cloud Services. While this works for most applications, in some cases you may need to override this default. You can do so by providing the UnifiedCredentialsOption The following example shows how to explicitly load a service account key file:
[](std::string const& keyfile) {
auto is = std::ifstream(keyfile);
is.exceptions(std::ios::badbit); // Minimal error handling in examples
auto contents = std::string(std::istreambuf_iterator<char>(is.rdbuf()), {});
auto options =
google::cloud::Options{}.set<google::cloud::UnifiedCredentialsOption>(
google::cloud::MakeServiceAccountCredentials(contents));
return google::cloud::optimization_v1::FleetRoutingClient(
google::cloud::optimization_v1::MakeFleetRoutingConnection(options));
}
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Missing the information I need","missingTheInformationINeed","thumb-down"],["Too complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14 UTC."],[[["\u003cp\u003eThis page provides documentation for overriding default authentication credentials in the C++ client libraries for Google Cloud services, covering versions from 2.11.0 up to the latest release candidate 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eBy default, the client libraries utilize Application Default Credentials for authentication, but users can override this behavior when needed.\u003c/p\u003e\n"],["\u003cp\u003eOverriding default credentials involves using \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e and, as an example, it is shown how to explicitly load a service account key file using \u003ccode\u003eMakeServiceAccountCredentials\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eUsers should consult the "Best practices for managing service account keys" guide for more detailed security information.\u003c/p\u003e\n"],["\u003cp\u003eFor further information on creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects, users can refer to the Authentication Components documentation.\u003c/p\u003e\n"]]],[],null,[]]