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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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 version-specific information ranging from 2.11.0 to the latest release candidate 2.37.0-rc.\u003c/p\u003e\n"],["\u003cp\u003eClient libraries typically use Application Default Credentials (ADC), but you can override this by providing the UnifiedCredentialsOption.\u003c/p\u003e\n"],["\u003cp\u003eA service account key file can be loaded to override the default credentials, as demonstrated in the provided code example that shows the use of \u003ccode\u003egoogle::cloud::UnifiedCredentialsOption\u003c/code\u003e and \u003ccode\u003egoogle::cloud::MakeServiceAccountCredentials\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eFor security, it is recommended that you review the "Best practices for managing service account keys" guide.\u003c/p\u003e\n"],["\u003cp\u003eYou can find further details on creating \u003ccode\u003egoogle::cloud::Credentials\u003c/code\u003e objects within the "Authentication Components" section.\u003c/p\u003e\n"]]],[],null,[]]
