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::bigquerycontrol_v2::DatasetServiceClient(
google::cloud::bigquerycontrol_v2::MakeDatasetServiceConnectionRest(
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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 documents how to override the default Application Default Credentials (ADC) for authenticating with Google Cloud Services using the C++ client libraries.\u003c/p\u003e\n"],["\u003cp\u003eThe \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e can be used to provide custom authentication, like loading a service account key file, as shown in the example code.\u003c/p\u003e\n"],["\u003cp\u003eLinks to examples are available for various \u003ccode\u003e*Client\u003c/code\u003e classes, including \u003ccode\u003eDatasetServiceClient\u003c/code\u003e, \u003ccode\u003eJobServiceClient\u003c/code\u003e, and \u003ccode\u003eModelServiceClient\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eFor managing service account keys, refer to the best practices guide provided in the content, as this is essential information to keep in mind.\u003c/p\u003e\n"],["\u003cp\u003eThe page also provides a link to "Authentication Components" for more information on creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects, giving additional information about authentication.\u003c/p\u003e\n"]]],[],null,[]]
