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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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\u003eThis document provides a guide on how to override default authentication credentials when using Google Cloud C++ client libraries, which typically rely on Application Default Credentials.\u003c/p\u003e\n"],["\u003cp\u003eThe latest available version is \u003ccode\u003e2.37.0-rc\u003c/code\u003e, and there is a list of previous versions starting from \u003ccode\u003e2.36.0\u003c/code\u003e down to \u003ccode\u003e2.11.0\u003c/code\u003e for users to reference.\u003c/p\u003e\n"],["\u003cp\u003eUsers can override the default credentials by providing a \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e, such as loading a service account key file, which is demonstrated with example code.\u003c/p\u003e\n"],["\u003cp\u003eThe document provides links to examples for \u003ccode\u003evision_v1::ImageAnnotatorClient\u003c/code\u003e and \u003ccode\u003evision_v1::ProductSearchClient\u003c/code\u003e, and directs the user to best practices for managing service account keys.\u003c/p\u003e\n"],["\u003cp\u003eAdditional information about creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects can be found under the Authentication Components section.\u003c/p\u003e\n"]]],[],null,[]]
