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::accesscontextmanager_v1::AccessContextManagerClient(
google::cloud::accesscontextmanager_v1::
MakeAccessContextManagerConnection(options));
}
[[["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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 available version is 2.37.0-rc, with numerous other versions, starting at 2.11.0, also available for review, all linked to documentation on overriding authentication.\u003c/p\u003e\n"],["\u003cp\u003eClient libraries default to using Application Default Credentials for authenticating with Google Cloud Services, but this can be overridden when necessary.\u003c/p\u003e\n"],["\u003cp\u003eOverriding the default authentication can be done by providing the UnifiedCredentialsOption, as shown in the example with explicitly loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eThe example provided demonstrates a method for loading a service account key file and is for illustrative purposes, recommending readers to consult best practices for managing service account keys.\u003c/p\u003e\n"],["\u003cp\u003eAdditional information on factory functions to create \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects can be found in the Authentication Components section.\u003c/p\u003e\n"]]],[],null,[]]
