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::dataproc_v1::AutoscalingPolicyServiceClient(
google::cloud::dataproc_v1::MakeAutoscalingPolicyServiceConnection(
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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-07-09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 provides documentation for overriding default authentication credentials when using Google Cloud client libraries, specifically focusing on the `UnifiedCredentialsOption`."],["The latest version documented is 2.37.0-rc, and this document lists versions down to 2.11.0 with the latest, and prior versions linked for easy navigation to prior documentation."],["The default authentication uses Application Default Credentials, but the process for overriding this by loading a service account key file using `UnifiedCredentialsOption` is demonstrated in the code example."],["Links to specific `*Client` classes (e.g., `AutoscalingPolicyServiceClient`, `BatchControllerClient`) with service account examples are available for the 2.18.0 version."],["There are relevant links for further information on authentication, and best practices for managing service account keys."]]],[]]
