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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 page provides documentation for overriding default authentication credentials when using Google Cloud C++ client libraries for the Vision API, with the latest version being \u003ccode\u003e2.37.0-rc\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eThe \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e allows users to specify custom authentication methods, such as loading a service account key file, instead of relying on Application Default Credentials.\u003c/p\u003e\n"],["\u003cp\u003eExamples are available for \u003ccode\u003evision_v1::ImageAnnotatorClient\u003c/code\u003e and \u003ccode\u003evision_v1::ProductSearchClient\u003c/code\u003e classes, demonstrating how to implement service account authentication.\u003c/p\u003e\n"],["\u003cp\u003eThe provided documentation covers multiple versions of the Vision API, starting from version \u003ccode\u003e2.11.0\u003c/code\u003e up to \u003ccode\u003e2.37.0-rc\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eRefer to the Best practices for managing service account keys guide and the Authentication components section for further information.\u003c/p\u003e\n"]]],[],null,[]]
