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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 page details how to override the default Application Default Credentials (ADC) for authenticating with Google Cloud Services, which is sometimes necessary.\u003c/p\u003e\n"],["\u003cp\u003eYou can override the default credentials by providing the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e, as demonstrated in the example that loads a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eThe document provides links to examples for other client classes, such as \u003ccode\u003etrace_v1::TraceServiceClient\u003c/code\u003e and \u003ccode\u003etrace_v2::TraceServiceClient\u003c/code\u003e, related to the trace override authentication.\u003c/p\u003e\n"],["\u003cp\u003eThe page offers a comprehensive list of available versions, from 2.11.0 up to the latest release candidate 2.37.0-rc, for reference and specific client implementation needs.\u003c/p\u003e\n"],["\u003cp\u003eFor best practices regarding service account keys, please consult the linked guide, which is provided for more in-depth considerations.\u003c/p\u003e\n"]]],[],null,[]]
