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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 in Google Cloud C++ client libraries for various versions, starting from version 2.11.0 up to the latest release candidate 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eThe client libraries typically use Application Default Credentials (ADC), but users can override this by utilizing \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e to specify alternative credentials.\u003c/p\u003e\n"],["\u003cp\u003eThe example illustrates overriding with a service account key file, showing how to read the key file content and create a \u003ccode\u003eManagedIdentitiesServiceClient\u003c/code\u003e with custom credentials.\u003c/p\u003e\n"],["\u003cp\u003eFor more details and best practices on managing service account keys, users should refer to the provided documentation link.\u003c/p\u003e\n"],["\u003cp\u003eFurther information on creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects can be found in the "Authentication Components" section of the documentation.\u003c/p\u003e\n"]]],[],null,[]]
