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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 when using Google Cloud client libraries, with version 2.15.1 being the focal point.\u003c/p\u003e\n"],["\u003cp\u003eThe latest release candidate, version 2.37.0-rc, and multiple previous versions, are listed, with a full history of previous versions dating back to version 2.11.0.\u003c/p\u003e\n"],["\u003cp\u003eClient libraries typically use Application Default Credentials, but users can override this by using the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e to load a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eExamples for overriding authentication credentials are provided for various \u003ccode\u003e*Client\u003c/code\u003e classes, including \u003ccode\u003eApplicationsClient\u003c/code\u003e, \u003ccode\u003eAuthorizedCertificatesClient\u003c/code\u003e, \u003ccode\u003eAuthorizedDomainsClient\u003c/code\u003e, and others.\u003c/p\u003e\n"],["\u003cp\u003eThe documentation recommends reviewing the "Best practices for managing service account keys" guide for further details on service account key management.\u003c/p\u003e\n"]]],[],null,[]]
