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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 various versions of the Google Cloud C++ client library for App Engine, ranging from version 2.11.0 to the latest release candidate 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eThe documentation explains how to override the default authentication credentials (Application Default Credentials) used by the client libraries.\u003c/p\u003e\n"],["\u003cp\u003eUsers can override the default by providing the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e, demonstrated by loading a service account key file explicitly.\u003c/p\u003e\n"],["\u003cp\u003eThe page provides links to examples for various \u003ccode\u003e*Client\u003c/code\u003e classes within the \u003ccode\u003eappengine_v1\u003c/code\u003e namespace, detailing how to set up service account authentication for each one.\u003c/p\u003e\n"],["\u003cp\u003eThe documentation directs users to further resources, including best practices for managing service account keys and authentication components.\u003c/p\u003e\n"]]],[],null,[]]
