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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-07-09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 provides documentation for overriding default authentication credentials when using Google Cloud client libraries, which typically rely on Application Default Credentials."],["You can override the default credentials by providing the `UnifiedCredentialsOption`, as demonstrated with an example of loading a service account key file."],["The provided examples showcase how to override authentication for several client classes, including `ApplicationsClient`, `AuthorizedCertificatesClient`, `AuthorizedDomainsClient`, `DomainMappingsClient`, `FirewallClient`, `InstancesClient`, `ServicesClient`, and `VersionsClient`."],["The latest available release candidate version for the reference documentation is 2.37.0-rc, but there are multiple other versions ranging from 2.36.0 to 2.11.0."],["For further details and best practices regarding service account key management, refer to the linked \"Best practices for managing service account keys\" guide."]]],[]]
