HMAC-SHA256: XPayLabs API Authentication Reference

Every API request to XPayLabs must include a cryptographic signature. This page details the exact signing algorithm, the purpose of each field, and common pitfalls.

Signing Algorithm

The sign field is computed as:

sign = HEX(HMAC-SHA256(JSON.stringify(data), merchant_token))

Where:

data is the request body payload (the data field of ReqPayload)
merchant_token is your configured secret token
HMAC-SHA256 produces a binary digest
HEX converts it to a lowercase hexadecimal string (64 characters)

Important: JSON Serialization

The data object must be serialized to JSON with no extra whitespace. Different JSON libraries may produce different output:

Library	Output	Valid?
`JSON.stringify(obj)`	`{"amount":"100.00","symbol":"USDT","chain":"TRON"}`	✅ Yes
`json.dumps(obj, separators=(",",":"))`	`{"amount":"100.00","symbol":"USDT","chain":"TRON"}`	✅ Yes
`json.dumps(obj, indent=2)`	Formatted with spaces/newlines	❌ No

The signature is computed over the data field only — not over the full ReqPayload envelope. The sign, timestamp, and nonce fields are excluded from signing.

Request Envelope

Each request must include these four fields as a JSON object:

{
  "sign": "a1b2c3d4e5f6...",
  "timestamp": 1717000000,
  "nonce": "550e8400-e29b-41d4-a716-446655440000",
  "data": {
    "amount": "100.00",
    "symbol": "USDT",
    "chain": "TRON"
  }
}

Language Examples

Node.js

import crypto from "crypto";

function sortKeys(obj) {
  return Object.keys(obj)
    .sort()
    .reduce((acc, k) => {
      acc[k] = obj[k];
      return acc;
    }, {});
}

function signRequest(data, token) {
  return crypto
    .createHmac("sha256", token)
    .update(JSON.stringify(sortKeys(data)), "utf8")
    .digest("hex");
}

Python

import hmac, hashlib, json

def sign_request(data: dict, token: str) -> str:
    json_str = json.dumps(data, separators=(",", ":"), sort_keys=True)
    return hmac.new(token.encode(), json_str.encode(), hashlib.sha256).hexdigest()

Java

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

public static String signRequest(Object data, String token) throws Exception {
    ObjectMapper mapper = new ObjectMapper();
    mapper.enable(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS);
    String json = mapper.writeValueAsString(data);
    Mac mac = Mac.getInstance("HmacSHA256");
    mac.init(new SecretKeySpec(token.getBytes("UTF-8"), "HmacSHA256"));
    byte[] digest = mac.doFinal(json.getBytes("UTF-8"));
    return bytesToHex(digest);
}

Go

import (
    "crypto/hmac"
    "crypto/sha256"
    "encoding/hex"
    "encoding/json"
)

func SignRequest(data interface{}, token string) string {
    jsonBytes, _ := json.Marshal(data)  // compact JSON
    mac := hmac.New(sha256.New, []byte(token))
    mac.Write(jsonBytes)
    return hex.EncodeToString(mac.Sum(nil))
}

Verification

XPayLabs verifies each request by:

Recomputing the HMAC-SHA256 signature from the data field and your stored merchant token.
Checking that the computed signature matches the provided sign value.
Validating that the timestamp is within 5 minutes of the server clock.
Ensuring the nonce has not been used before.

If any check fails, the gateway returns a 401 Unauthorized response:

{
  "code": 401,
  "msg": "Sign verification failed",
  "data": null
}

GET Request Signing

For GET requests that require authentication (e.g., /v1/order/status/{orderId}, /v1/order/pay, /v1/order/getOrderStatus), the sign parameter is passed as a query string value. The signature is computed over the relevant parameters (typically orderId):

sign = HEX(HMAC-SHA256(orderId, merchant_token))

​Signing Algorithm

​Important: JSON Serialization

​Request Envelope

​Language Examples

​Node.js

​Python

​Java

​Go

​Verification

​GET Request Signing

Signing Algorithm

Important: JSON Serialization

Request Envelope

Language Examples

Node.js

Python

Java

Go

Verification

GET Request Signing