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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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, with a focus on Data Migration Service.\u003c/p\u003e\n"],["\u003cp\u003eThe latest release candidate for the Data Migration Service documentation is version 2.37.0-rc, with multiple previous versions available ranging back to version 2.11.0.\u003c/p\u003e\n"],["\u003cp\u003eThe default authentication method is Application Default Credentials, but the UnifiedCredentialsOption can be used to override this, for example, by loading a service account key file.\u003c/p\u003e\n"],["\u003cp\u003eThe provided example demonstrates how to explicitly load a service account key file for authentication, with a recommendation to refer to the best practices guide for managing service account keys.\u003c/p\u003e\n"],["\u003cp\u003eMore information on creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects can be found in the Authentication Components section of the documentation.\u003c/p\u003e\n"]]],[],null,[]]
