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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 lists various versions of the C++ optimization documentation, ranging from version 2.11.0 to the latest release candidate, 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eThe client libraries generally authenticate using Application Default Credentials, but this can be overridden.\u003c/p\u003e\n"],["\u003cp\u003eYou can override the default authentication by providing the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e, as demonstrated by the example code loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eFor in-depth details on creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects, refer to the "Authentication Components" section.\u003c/p\u003e\n"],["\u003cp\u003eThe example for overriding the default authentication in the documentation is easy to follow, but you should consult the best practices for managing service accounts for more information.\u003c/p\u003e\n"]]],[],null,[]]
