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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-07-09 UTC."],[[["This page details how to override the default Application Default Credentials for authenticating with Google Cloud Services, primarily by utilizing the `UnifiedCredentialsOption`."],["Version 2.37.0-rc is the latest available version, with multiple prior versions listed, including the currently selected version 2.24.0."],["The provided C++ code example demonstrates explicitly loading a service account key file to override authentication."],["The information and code example are relevant to multiple `*Client` classes, including `ApplicationsClient`, `AuthorizedCertificatesClient`, `AuthorizedDomainsClient`, `DomainMappingsClient`, `FirewallClient`, `InstancesClient`, `ServicesClient`, and `VersionsClient`."],["For further details, users are referred to the documentation on Authentication Components and the guide on Best practices for managing service account keys."]]],[]]
