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::functions_v1::CloudFunctionsServiceClient(
google::cloud::functions_v1::MakeCloudFunctionsServiceConnection(
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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 when using C++ client libraries.\u003c/p\u003e\n"],["\u003cp\u003eYou can override the default credentials by providing the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e, demonstrated with an example of loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eThe latest version available is 2.37.0-rc, and there are numerous prior releases, down to version 2.11.0, that have their respective documentation.\u003c/p\u003e\n"],["\u003cp\u003eExamples for overriding authentication are provided for both \u003ccode\u003efunctions_v1::CloudFunctionsServiceClient\u003c/code\u003e and \u003ccode\u003efunctions_v2::FunctionServiceClient\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eUsers are encouraged to consult the "Best practices for managing service account keys" guide for further security recommendations.\u003c/p\u003e\n"]]],[],null,[]]
