How will we receive a response from the payment provider? The interviewer suggests using a webhook.

Using a webhook to receive responses from a payment provider is a common and convenient way to get asynchronous notifications about the payment status.

How it works:

• You register your server URL (webhook) with the provider.
• After processing the payment, the provider sends an HTTP POST request to this URL with the result information.
• Your server receives the request, verifies the signature/authorization for security, and updates the payment status in the system.

Example in Go (simplified):

func paymentWebhookHandler(w http.ResponseWriter, r *http.Request) {
    // Check method
    if r.Method != http.MethodPost {
        http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
        return
    }

    // Read request body
    body, err := ioutil.ReadAll(r.Body)
    if err != nil {
        http.Error(w, "Bad request", http.StatusBadRequest)
        return
    }

    // Signature validation (depends on provider)
    if !validateSignature(r.Header, body) {
        http.Error(w, "Unauthorized", http.StatusUnauthorized)
        return
    }

    // Parse data
    var paymentStatus PaymentStatus
    if err := json.Unmarshal(body, &paymentStatus); err != nil {
        http.Error(w, "Bad request", http.StatusBadRequest)
        return
    }

    // Update payment status in database
    updatePaymentStatus(paymentStatus)

    w.WriteHeader(http.StatusOK)
}

Thus, a webhook allows real-time notifications without the need to poll the provider.