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::datamigration_v1::DataMigrationServiceClient(
google::cloud::datamigration_v1::MakeDataMigrationServiceConnection(
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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 provides documentation for overriding default authentication credentials when using Google Cloud client libraries, specifically in the context of C++ data migration.\u003c/p\u003e\n"],["\u003cp\u003eThe latest version available is 2.37.0-rc, but documentation is also accessible for numerous previous versions, including releases going back to version 2.11.0.\u003c/p\u003e\n"],["\u003cp\u003eUsers can override the default \u003ca href=\"https://cloud.google.com/docs/authentication#adc\"\u003eApplication Default Credentials\u003c/a\u003e by utilizing the \u003ca href=\"https://cloud.google.com/cpp/docs/reference/common/latest/structgoogle_1_1cloud_1_1UnifiedCredentialsOption.html\"\u003eUnifiedCredentialsOption\u003c/a\u003e.\u003c/p\u003e\n"],["\u003cp\u003eAn example is given demonstrating how to explicitly load a service account key file in order to override the default, however users should consult best practices for key management.\u003c/p\u003e\n"],["\u003cp\u003eAdditional details on creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects are found in the \u003ca href=\"https://cloud.google.com/cpp/docs/reference/common/latest/group__guac.html\"\u003eAuthentication Components\u003c/a\u003e documentation.\u003c/p\u003e\n"]]],[],null,[]]
