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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 client libraries, specifically focusing on the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eThe latest release candidate version is 2.37.0-rc, and a range of other versions, from 2.36.0 down to 2.11.0, are also documented, all of which include instructions for overriding the authentication.\u003c/p\u003e\n"],["\u003cp\u003eThe page demonstrates how to explicitly load a service account key file using the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e and the \u003ccode\u003eMakeServiceAccountCredentials\u003c/code\u003e function within the \u003ccode\u003egoogle::cloud\u003c/code\u003e namespace.\u003c/p\u003e\n"],["\u003cp\u003eExamples are available for different client classes like \u003ccode\u003eQuotaControllerClient\u003c/code\u003e and \u003ccode\u003eServiceControllerClient\u003c/code\u003e within various \u003ccode\u003eservicecontrol_v\u003c/code\u003e namespaces, with links to each being provided on the webpage.\u003c/p\u003e\n"],["\u003cp\u003eUsers are directed to the "Best practices for managing service account keys" guide for more in-depth details on service account key management and the "Authentication Components" page to better understand the \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects.\u003c/p\u003e\n"]]],[],null,[]]
