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::serviceusage_v1::ServiceUsageClient(
google::cloud::serviceusage_v1::MakeServiceUsageConnection(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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 webpage provides documentation for various versions of the C++ Service Usage client library, with the latest version being 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eThe client libraries use Application Default Credentials for authentication by default, but this can be overridden.\u003c/p\u003e\n"],["\u003cp\u003eTo override default authentication, you can use the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e, as demonstrated with an example of loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eThe \u003ccode\u003eAuthentication Components\u003c/code\u003e link and the \u003ccode\u003eBest practices for managing service account keys\u003c/code\u003e guide are provided for additional information on creating credentials and managing service account keys.\u003c/p\u003e\n"],["\u003cp\u003eThe content covers versions going all the way back to 2.11.0 of the C++ Service Usage Client Library.\u003c/p\u003e\n"]]],[],null,[]]
