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5. Verify payment information

Verify the payment information for secure payment service implementation.

Based on the payment information from the client, the server verifies the payment amount for fraud and saves the payment information in the database if needed. The following are the steps for verifying the payment information.

  • Server receives the iโ€™mport payment ID (imp_uid) and order ID (merchant_uid)
  • Call the Get payment API to get the payment details.
  • Based on the response, compare the actual payment amount with the payment request amount (from merchantโ€™s database).

STEP 01 Server receives payment result

Example of receiving a POST request to the merchant endpoint URL that receives the payment information

server-side
app.use(bodyParser.json()); // "{Merchant endpoint that receives server's payment info}" POST request receiver app.post("/payments/complete", async (req, res) => { try { // Get imp_uid, merchant_uid from req.body const { imp_uid, merchant_uid } = req.body; } catch (e) { res.status(400).send(e); } });

STEP 02 Get payment details

Example of calling the Get payment API with the iโ€™mport payment ID (imp_uid) to retrieve the payment info.

server-side
app.use(bodyParser.json()); ... app.post("/payments/complete", async (req, res) => { try { // Get imp_uid, merchant_uid from req.body const { imp_uid, merchant_uid } = req.body; ... // Get access token const getToken = await axios({ url: "https://api.iamport.kr/users/getToken", method: "post", // POST method headers: { "Content-Type": "application/json" }, data: { imp_key: "imp_apikey", // REST API key imp_secret: "ekKoeW8RyKuT0zgaZsUtXXTLQ4AhPFW3ZGseDA6bkA5lamv9OqDMnxyeB9wqOsuO9W3Mx9YSJ4dTqJ3f" // REST API Secret } }); const { access_token } = getToken.data.response; // access token ... // Get payment info from i'mport server using imp_uid const getPaymentData = await axios({ // Pass imp_uid url: \`https://api.iamport.kr/payments/\${imp_uid}\`, // GET method method: "get", // Add access toke to Authorization header headers: { "Authorization": access_token } }); const paymentData = getPaymentData.data.response; // Payment info ... } catch (e) { res.status(400).send(e); } });

STEP 03 Verify payment information

Why fraud detection is necessary

Since the payment request is made on the client side, a payment request can be forged or falsified by manipulating the client script. Therefore, you must compare the original requested amount with the actual processed amount after the payment process is complete.

For example, when paying for a product that costs 100,000 won, an attacker can manipulate the client script to change the amount property to a value lower than the actual amount.

Since you cannot prevent script manipulation on the client, you must check for fraud on the server after the payment is processed.

Example of comparing the actual payment amount with the payment request amount, performing fraud check on the payment amount, and saving the data in the DB.

server-side
app.use(bodyParser.json()); ... app.post("/payments/complete", async (req, res) => { try { // Get imp_uid, merchant_uid from req.body const { imp_uid, merchant_uid } = req.body; // Get access token /* ...Omitted... */ // Get payment info from iamport server using imp_uid /* ...Omitted... */ const paymentData = getPaymentData.data.response; // Payment info ... // Get the requested payment amount from the DB const order = await Orders.findById(paymentData.merchant_uid); const amountToBePaid = order.amount; // Requested payment amount ... // Verify payment const { amount, status } = paymentData; // If amount matches. Processed amount === Requested amount if (amount === amountToBePaid) { await Orders.findByIdAndUpdate(merchant_uid, { $set: paymentData }); // Save payment info to DB ... switch (status) { case "ready": // Issue virtual account // Save virtual account info in DB const { vbank_num, vbank_date, vbank_name } = paymentData; await Users.findByIdAndUpdate("/* customer id */", { $set: { vbank_num, vbank_date, vbank_name }}); // Send virtual account issuance text message SMS.send({ text: \`Virtual account issued successfully. Account info \${vbank_num} \${vbank_date} \${vbank_name}\`}); res.send({ status: "vbankIssued", message: "Virtual account issued successfully" }); break; case "paid": // Payment complete res.send({ status: "success", message: "General payment successful" }); break; } } else { // Amount mismatch. Forged/falsified payment. throw { status: "forgery", message: "Forged/falsified payment attempted" }; } } catch (e) { res.status(400).send(e); } });

The original requested amount is queried from the database with the merchant_uid, and the actual processed amount is retrieved from the iโ€™mport server with the imp_uid. The two values are compared to verify that they match. If the verification is successful, the payment information is saved in the database and a response is returned based on the payment status (status). Otherwise, an error message is returned.\

The payment result must be processed on the database based on the data received through a webhook for stable processing without any missing result data.