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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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, specifically focusing on the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eThe latest version documented is 2.37.0-rc, and documentation spans back to version 2.11.0, covering several prior releases.\u003c/p\u003e\n"],["\u003cp\u003eThe example demonstrates loading a service account key file to override default credentials using \u003ccode\u003eMakeServiceAccountCredentials\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eLinks to service account examples are provided for multiple \u003ccode\u003e*Client\u003c/code\u003e classes, such as \u003ccode\u003eApplicationsClient\u003c/code\u003e, \u003ccode\u003eAuthorizedCertificatesClient\u003c/code\u003e, and \u003ccode\u003eVersionsClient\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eDefault credentials for client libraries use Application Default Credentials, which can be overridden if needed for more specific use cases, and there are best practices to keep in mind when working with service accounts.\u003c/p\u003e\n"]]],[],null,[]]
