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::essentialcontacts_v1::EssentialContactsServiceClient(
google::cloud::essentialcontacts_v1::
MakeEssentialContactsServiceConnection(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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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\u003eThe latest version available is 2.37.0-rc, with numerous older versions available down to 2.12.0.\u003c/p\u003e\n"],["\u003cp\u003eClient libraries typically use Application Default Credentials for Google Cloud Service authentication, but this can be overridden.\u003c/p\u003e\n"],["\u003cp\u003eYou can override default authentication by providing the UnifiedCredentialsOption, such as loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eThe example code demonstrates overriding authentication by loading a service account key file's contents and setting it within the UnifiedCredentialsOption.\u003c/p\u003e\n"],["\u003cp\u003eFor more information about managing service accounts key and best practices, consult the \u003ca href=\"https://cloud.google.com/iam/docs/best-practices-for-managing-service-account-keys\"\u003eBest practices for managing service account keys\u003c/a\u003e guide.\u003c/p\u003e\n"]]],[],null,[]]
