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::essentialcontacts_v1::EssentialContactsServiceClient(
google::cloud::essentialcontacts_v1::
MakeEssentialContactsServiceConnection(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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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\u003eThe webpage provides documentation for various versions of the C++ client library, ranging from version 2.12.0 to the latest release candidate 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eThe client libraries use Application Default Credentials for authentication with Google Cloud Services unless otherwise specified.\u003c/p\u003e\n"],["\u003cp\u003eYou can override the default authentication method by using the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e, for instance, loading credentials from a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eThe example shows how to load a service account key file to override the default credentials, while best practices for managing keys should be consulted for production systems.\u003c/p\u003e\n"],["\u003cp\u003eThe document provides a reference to Authentication Components for creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects.\u003c/p\u003e\n"]]],[],null,[]]
