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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 document provides a guide on how to override default authentication credentials when using Google Cloud Client Libraries, using a service account key file as an example.\u003c/p\u003e\n"],["\u003cp\u003eThe latest available version is 2.37.0-rc, and this document includes a list of version-specific links dating back to version 2.11.0 for reference on overriding authentication.\u003c/p\u003e\n"],["\u003cp\u003eThe client libraries typically use Application Default Credentials (ADC) for authentication, but \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e allows for overriding this default.\u003c/p\u003e\n"],["\u003cp\u003eExamples are available for \u003ccode\u003eQuotaControllerClient\u003c/code\u003e, and \u003ccode\u003eServiceControllerClient\u003c/code\u003e classes.\u003c/p\u003e\n"],["\u003cp\u003eIt's important to consult the "Best practices for managing service account keys" guide for detailed service account management advice, along with the "Authentication Components" for more information about creating credentials.\u003c/p\u003e\n"]]],[],null,[]]
