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::vision_v1::ImageAnnotatorClient(
google::cloud::vision_v1::MakeImageAnnotatorConnection(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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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\u003eThe latest version available is 2.37.0-rc, with numerous prior versions available down to 2.11.0.\u003c/p\u003e\n"],["\u003cp\u003eClient libraries typically use Application Default Credentials for Google Cloud Service authentication, but this can be overridden.\u003c/p\u003e\n"],["\u003cp\u003eAuthentication can be overridden by providing the UnifiedCredentialsOption, demonstrated through explicitly loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eExamples are available for \u003ccode\u003evision_v1::ImageAnnotatorClient\u003c/code\u003e and \u003ccode\u003evision_v1::ProductSearchClient\u003c/code\u003e to illustrate overriding authentication with service accounts.\u003c/p\u003e\n"],["\u003cp\u003eThe Authentication Components section provides more information on the factory functions to create Credentials objects, and the guide on managing service account keys should be consulted.\u003c/p\u003e\n"]]],[],null,[]]
