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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 C++ client libraries for App Engine services, starting with version 2.11.0 and going up to the latest, 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eThe default authentication method for client libraries is Application Default Credentials, but you can override it by using the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e with a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eExamples are provided to load a service account key file, and they illustrate how to apply this to various client classes, including \u003ccode\u003eApplicationsClient\u003c/code\u003e, \u003ccode\u003eAuthorizedCertificatesClient\u003c/code\u003e, and \u003ccode\u003eVersionsClient\u003c/code\u003e, among others.\u003c/p\u003e\n"],["\u003cp\u003eThe page also references the best practices guide for managing service account keys and the authentication components for creating credential objects.\u003c/p\u003e\n"]]],[],null,[]]
