Skeleton code

function get_bango_id () {
    // *Always* use this endpoint prefix for the Bango Payment API.
    const base_url = "https://api.bango.net/v5/";

    // This is what we're trying to find.
    let bango_id = null;

    try {
        // We start without a session ID. The first request will allocate one,
        // which we reuse in subsequent requests until we reach a terminal state.
        let session_id = '';

        // Flag which is set true when we can't perform a requested action.
        let send_cancel = false;

        const request_body_params = {
            // Add request parameters as necessary here
        };

        while (bango_id == null) {
            // Tell the Bango Platform we can't perform
            // the requested action if necessary.
            if (send_cancel) {
                request_body_params.set("action", "cancel");
                send_cancel = false;
            } else {
                request_body_params.delete('action');
            }

            // POST UTF-8 JSON to the Bango Payment API and parse the JSON response
            let response = rest_client_call({
                method: "POST",
                url: base_url + "identity/" + session_id,
                headers: {
                    "Authorization": get_authorization_header(),
                    "Content-Type": "application/json",
                },
                body: make_json_string(request_body_params),
            }).from_json();

            // The responseCode tells us what to do next.
            switch (response.responseCode) {
                // Success: we have the identity.
                case "OK":
                    bango_id = response.bangoUserId;
                    break;

                // Failure: unable to identify the user.
                case "USER_CANCELLED": // User declined to supply details
                case "NOT_AVAILABLE": // No identification methods were found
                    throw "User cannot be identified";

                // Merchant problems
                // These indicate issues in your code, not the Bango Platform.
                case "BAD_REQUEST":   // Invalid request
                case "UNAUTHORIZED":  // Check your credentials
                case "NOT_FOUND":     // Invalid session ID, or session expired
                    throw "Merchant implementation error";

                // Bango Platform issues
                // These likely indicate transient problems.
                // In production code, you might want to try the request again
                // after a delay, ultimately falling back to an error state.
                case "INTERNAL_ERROR":
                case "CONNECT_ERROR":
                case "FAILURE":
                case "SERVICE_UNAVAILABLE":
                case "CONNECT_TIMEOUT":
                    throw "Bango Platform unavailable"

                // More to do: The store must take action, then send another request
                case "CLIENT_ACTION_REQUIRED":
                    // This response parameter tells us what we need to do.
                    switch (response.parameters.action) {
                        case "REDIRECT":
                            // Send the user to a particular web page.
                            redirect_device_to({
                                url: response.parameters.url,
                            });
                            break;

                        case "SEND_SMS":
                            // Send an SMS on behalf of the user.
                            send_sms_from_device({
                                message: response.parameters.text,
                                to: response.parameters.shortcode,
                            });
                            break;

                        case "WAIT":
                            // Wait for a short period of time.
                            sleep({
                                milliseconds: response.parameters.suggestedWaitTimeMilliseconds,
                            });
                            break;

                        default:
                            // Unrecognized action. In the next request,
                            // we ask the Bango Platform to use a different method.
                            send_cancel = true;
                            break;
                    }

                    break;

                // This might indicate Bango has added a new response code.
                // Check the documentation again.
                default:
                    throw "Unrecognized response code";
            }

            // The Bango Platform has allocated an ID for this identification session.
            session_id = response.sessionId;
        }

    } catch (exception) {
        // Production code might want to notify the merchant in some way,
        // and/or log full details of the exception for later analysis,
        // and degrade gracefully for the user.
        output("An error occurred!");
        output(exception);
    }

    return bango_id;
}