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::discoveryengine_v1::CompletionServiceClient(
google::cloud::discoveryengine_v1::MakeCompletionServiceConnection(
options));
}
Follow these links to find examples for other *Client classes:
[[["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complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-14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."],[[["This page details how to override the default authentication credentials used by the client libraries when interacting with Google Cloud Services, which typically rely on Application Default Credentials."],["The provided example demonstrates overriding the default credentials by explicitly loading a service account key file using `UnifiedCredentialsOption`."],["There is a list of available versions, from the most recent release candidate `2.37.0-rc` down to `2.15.1`, and all use the `discoveryengine-override-authentication` file."],["Links to examples for different `*Client` classes, such as `CompletionServiceClient`, `ConversationalSearchServiceClient`, and others, are provided to show how to apply the service account override for those clients."],["The page suggests consulting the \"Best practices for managing service account keys\" guide for additional information on managing service account keys, with a pointer to authentication component documentation."]]],[]]
