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::essentialcontacts_v1::EssentialContactsServiceClient(
google::cloud::essentialcontacts_v1::
MakeEssentialContactsServiceConnection(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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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, ranging from 2.36.0 down to 2.12.0, also accessible.\u003c/p\u003e\n"],["\u003cp\u003eClient libraries typically authenticate with Google Cloud Services using Application Default Credentials, but users can override this default behavior.\u003c/p\u003e\n"],["\u003cp\u003eOverriding the default authentication can be accomplished by using the UnifiedCredentialsOption, demonstrated with an example of loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eFor best practices on managing service account keys, users are directed to the specified guide.\u003c/p\u003e\n"],["\u003cp\u003eUsers can see the Authentication Components documentation for more information about the functions to create google::cloud::Credentials objects.\u003c/p\u003e\n"]]],[],null,[]]
