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::language_v1::LanguageServiceClient(
google::cloud::language_v1::MakeLanguageServiceConnection(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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14 UTC."],[[["\u003cp\u003eThis page provides documentation for overriding default authentication credentials when using Google Cloud C++ client libraries.\u003c/p\u003e\n"],["\u003cp\u003eThe latest version covered is 2.37.0-rc, with multiple previous versions available for reference down to version 2.11.0.\u003c/p\u003e\n"],["\u003cp\u003eAuthentication overrides are achieved by using the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e, as demonstrated by loading a service account key file in the example code.\u003c/p\u003e\n"],["\u003cp\u003eThe example code shows how to use a service account file to authenticate via \u003ccode\u003eMakeServiceAccountCredentials\u003c/code\u003e, which can be used in multiple \u003ccode\u003e*Client\u003c/code\u003e classes, including \u003ccode\u003elanguage_v1::LanguageServiceClient\u003c/code\u003e and \u003ccode\u003elanguage_v2::LanguageServiceClient\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eFor best practices regarding service account key management and additional details on creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects, users are directed to relevant external resources.\u003c/p\u003e\n"]]],[],null,[]]
