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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 release candidate version is 2.37.0-rc, with version 2.30.0 being the currently presented version.\u003c/p\u003e\n"],["\u003cp\u003eClient libraries typically utilize Application Default Credentials for Google Cloud Services authentication, but can be overridden.\u003c/p\u003e\n"],["\u003cp\u003eYou can override default authentication by using the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e to load a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eExamples of overriding authentication credentials are provided for \u003ccode\u003evision_v1::ImageAnnotatorClient\u003c/code\u003e and \u003ccode\u003evision_v1::ProductSearchClient\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eRefer to the "Best practices for managing service account keys" guide for detailed information and the Authentication Components for information on creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e.\u003c/p\u003e\n"]]],[],null,[]]
