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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-07-09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."],[[["The latest version available is 2.37.0-rc, with numerous other versions from 2.36.0 to 2.11.0 also accessible via the provided links."],["The client libraries use Application Default Credentials for authentication with Google Cloud Services unless explicitly configured otherwise."],["Users can override default credentials by providing the UnifiedCredentialsOption, as demonstrated by loading a service account key file."],["Code examples are available for multiple `*Client` classes, such as `appengine_v1::ApplicationsClient`, `appengine_v1::AuthorizedCertificatesClient`, and more, to show how to override credentials."],["For in depth information, refer to the Best practices for managing service account keys guide and the Authentication Components documentation, which includes details on the `google::cloud::Credentials` objects."]]],[]]
