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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 version-specific documentation for overriding authentication credentials in Google Cloud C++ client libraries, including links for versions ranging from 2.11.0 to 2.36.0, and also 2.37.0-rc as the latest release candidate.\u003c/p\u003e\n"],["\u003cp\u003eThe client libraries primarily use Application Default Credentials for authentication, but you can override this by providing the UnifiedCredentialsOption.\u003c/p\u003e\n"],["\u003cp\u003eAn example demonstrates explicitly loading a service account key file to override the default authentication.\u003c/p\u003e\n"],["\u003cp\u003eSpecific examples for overriding authentication are provided for \u003ccode\u003etrace_v1::TraceServiceClient\u003c/code\u003e and \u003ccode\u003etrace_v2::TraceServiceClient\u003c/code\u003e classes.\u003c/p\u003e\n"],["\u003cp\u003eFor more information on managing service account keys, consult the recommended best practices guide, and additional details on creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e can be found in the Authentication Components section.\u003c/p\u003e\n"]]],[],null,[]]
