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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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\u003eThis page documents the C++ client library versions for Access Context Manager, ranging from the latest release candidate, 2.37.0-rc, down to version 2.11.0.\u003c/p\u003e\n"],["\u003cp\u003eThe client libraries use Application Default Credentials for authentication by default, but these can be overridden when needed.\u003c/p\u003e\n"],["\u003cp\u003eAuthentication credentials can be overridden by providing the UnifiedCredentialsOption, such as loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eThe example shows how to load a service account key file to override default authentication, but it's important to follow the best practices guide for managing service account keys.\u003c/p\u003e\n"],["\u003cp\u003eMore information about creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects can be found in the Authentication Components section.\u003c/p\u003e\n"]]],[],null,[]]
