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::servicecontrol_v1::QuotaControllerClient(
google::cloud::servicecontrol_v1::MakeQuotaControllerConnection(
options));
}
Follow these links to find examples for other *Client classes:
[[["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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 when using Google Cloud C++ client libraries.\u003c/p\u003e\n"],["\u003cp\u003eThe latest version documentation is for 2.37.0-rc, but the page lists multiple past version numbers from 2.36.0 down to 2.11.0.\u003c/p\u003e\n"],["\u003cp\u003eClient libraries generally use Application Default Credentials, but you can override this with the UnifiedCredentialsOption, shown through an example using a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eExamples of overriding authentication are provided for \u003ccode\u003eservicecontrol_v1::QuotaControllerClient\u003c/code\u003e, \u003ccode\u003eservicecontrol_v1::ServiceControllerClient\u003c/code\u003e, and \u003ccode\u003eservicecontrol_v2::ServiceControllerClient\u003c/code\u003e classes.\u003c/p\u003e\n"],["\u003cp\u003eThe provided documentation links to additional resources like the "Best practices for managing service account keys" and "Authentication Components" for a deeper understanding of authentication.\u003c/p\u003e\n"]]],[],null,[]]
