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::managedidentities_v1::ManagedIdentitiesServiceClient(
google::cloud::managedidentities_v1::
MakeManagedIdentitiesServiceConnection(options));
}
[[["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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 C++ client libraries for Managed Identities.\u003c/p\u003e\n"],["\u003cp\u003eThe latest release is version 2.37.0-rc, and the page contains links to previous versions, starting from 2.36.0 down to 2.11.0 of this library.\u003c/p\u003e\n"],["\u003cp\u003eClient libraries typically use Application Default Credentials (ADC), but users can override this by providing the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e, such as loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eThe example demonstrates how to load service account credentials from a key file using \u003ccode\u003eMakeServiceAccountCredentials\u003c/code\u003e, but users are encouraged to refer to the best practices guide for managing service account keys.\u003c/p\u003e\n"],["\u003cp\u003eThe Authentication Components section is referenced for more information on creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects using factory functions.\u003c/p\u003e\n"]]],[],null,[]]
