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::appengine_v1::ApplicationsClient(
google::cloud::appengine_v1::MakeApplicationsConnection(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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 provides documentation for overriding default authentication credentials in Google Cloud client libraries, specifically for the App Engine service, with the latest release candidate version being 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eThe default authentication for client libraries utilizes Application Default Credentials, but users can override this by providing a \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e, demonstrated with a service account key file example.\u003c/p\u003e\n"],["\u003cp\u003eExamples for various \u003ccode\u003e*Client\u003c/code\u003e classes are provided, such as \u003ccode\u003eApplicationsClient\u003c/code\u003e, \u003ccode\u003eAuthorizedCertificatesClient\u003c/code\u003e, and \u003ccode\u003eVersionsClient\u003c/code\u003e, showcasing how to apply the service account override for each.\u003c/p\u003e\n"],["\u003cp\u003eThe page includes a reference to the "Best practices for managing service account keys" guide and the "Authentication Components" documentation for more comprehensive details.\u003c/p\u003e\n"],["\u003cp\u003eThe documentation covers client library versions from 2.11.0 to 2.37.0-rc.\u003c/p\u003e\n"]]],[],null,[]]
