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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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, which normally use Application Default Credentials.\u003c/p\u003e\n"],["\u003cp\u003eYou can override the default authentication by using the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e and explicitly loading a service account key file as shown in the provided example code.\u003c/p\u003e\n"],["\u003cp\u003eThe page lists and links to examples demonstrating credential override for various \u003ccode\u003e*Client\u003c/code\u003e classes in the \u003ccode\u003eappengine_v1\u003c/code\u003e namespace, offering practical guidance.\u003c/p\u003e\n"],["\u003cp\u003eVersion history for the App Engine documentation is available, starting from version 2.11.0, and going up to the latest release candidate which is 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eThe page directs users to additional resources for best practices on service account key management and authentication components, providing comprehensive guidance.\u003c/p\u003e\n"]]],[],null,[]]
