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::trace_v1::TraceServiceClient(
google::cloud::trace_v1::MakeTraceServiceConnection(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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 Application Default Credentials as the default method of authentication.\u003c/p\u003e\n"],["\u003cp\u003eThe latest release candidate (rc) version available is 2.37.0-rc, with stable releases ranging from 2.36.0 down to 2.11.0, all providing examples of trace override authentication.\u003c/p\u003e\n"],["\u003cp\u003eYou can override default credentials by setting the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e, shown with an example that demonstrates loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eThe document includes examples for \u003ccode\u003etrace_v1::TraceServiceClient\u003c/code\u003e and \u003ccode\u003etrace_v2::TraceServiceClient\u003c/code\u003e classes, showing how to implement service account credentials.\u003c/p\u003e\n"],["\u003cp\u003eIt is recommended to consult the "Best practices for managing service account keys" guide for further details on managing service account keys.\u003c/p\u003e\n"]]],[],null,[]]
