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::vpcaccess_v1::VpcAccessServiceClient(
google::cloud::vpcaccess_v1::MakeVpcAccessServiceConnection(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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 version available is 2.37.0-rc, with numerous preceding versions from 2.36.0 down to 2.11.0 also documented.\u003c/p\u003e\n"],["\u003cp\u003eClient libraries generally authenticate using Application Default Credentials, but this can be overridden when needed.\u003c/p\u003e\n"],["\u003cp\u003eYou can override default credentials by providing the UnifiedCredentialsOption, such as explicitly loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eThe provided code example demonstrates how to load credentials from a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eRefer to the Authentication Components documentation for more on creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects.\u003c/p\u003e\n"]]],[],null,[]]
