Your application is authenticating by using local Application Default Credentials. The identitytoolkit.googleapis.com API requires a quota project, which is not set by default. To learn how to set your quota project, see https://cloud.google.com/docs/authentication/adc-troubleshooting/user-creds .

    /**
     * Append additional headers, e.g., x-goog-user-project, shared across the
     * classes inheriting AuthClient. This method should be used by any method
     * that overrides getRequestMetadataAsync(), which is a shared helper for
     * setting request information in both gRPC and HTTP API calls.
     *
     * @param headers object to append additional headers to.
     */
    addSharedMetadataHeaders(headers) {
        // quota_project_id, stored in application_default_credentials.json, is set in
        // the x-goog-user-project header, to indicate an alternate account for
        // billing and quota:
        if (!headers['x-goog-user-project'] && // don't override a value the user sets.
            this.quotaProjectId) {
            headers['x-goog-user-project'] = this.quotaProjectId;
        }
        return headers;
    }