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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 version-specific documentation for the C++ Vision API, ranging from version 2.11.0 up to the release candidate 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eThe primary focus of this page is to demonstrate how to override the default authentication credentials by supplying a service account key file using the \u003ccode\u003eUnifiedCredentialsOption\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eThe document references examples using the \u003ccode\u003eImageAnnotatorClient\u003c/code\u003e and \u003ccode\u003eProductSearchClient\u003c/code\u003e classes within the Vision API to exemplify how to use a service account for authentication.\u003c/p\u003e\n"],["\u003cp\u003eThe use of \u003ccode\u003eApplication Default Credentials\u003c/code\u003e is discussed, which works for most applications but can be overridden when needed, as detailed in the example and related documentation.\u003c/p\u003e\n"],["\u003cp\u003eIt also recommends reviewing the \u003ccode\u003eBest practices for managing service account keys\u003c/code\u003e for more details on managing keys and provides a link to \u003ccode\u003eAuthentication Components\u003c/code\u003e to understand how to create credentials.\u003c/p\u003e\n"]]],[],null,[]]
