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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 document provides a list of versioned documentation for C++ optimization reference, ranging from version 2.11.0 up to the latest release candidate, 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eThe primary focus of this page is on how to override the default authentication credentials used by client libraries when interacting with Google Cloud Services.\u003c/p\u003e\n"],["\u003cp\u003eUsers can override the default authentication using \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e, demonstrated via an example of loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eThe example code utilizes \u003ccode\u003egoogle::cloud::UnifiedCredentialsOption\u003c/code\u003e and \u003ccode\u003egoogle::cloud::MakeServiceAccountCredentials\u003c/code\u003e to explicitly set authentication credentials, offering an alternative to Application Default Credentials.\u003c/p\u003e\n"],["\u003cp\u003eThe document also points readers towards the "Authentication Components" section for creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e and the "Best practices for managing service account keys" guide for further authentication details.\u003c/p\u003e\n"]]],[],null,[]]
