POST /your_uri HTTP/1.1
host: your.host
accept: application/json
content-type: application/json
content-length: 165
authorization: Signature 52eac2713985e212351610d008e7e14fae46f902
{
  "notification_type":"user_validation",
  "user":{
      "ip":"127.0.0.1",
      "phone":"18777976552",
      "email":"email@example.com",
      "id":1234567,
      "name":"Xsolla User",
      "country":"US"
  }
}

curl -v 'https://your.hostname/your/uri' \
-X POST \
-H 'authorization: Signature 52eac2713985e212351610d008e7e14fae46f902' \
-d '{
  "notification_type":
    "user_validation",
    "user":
      {
        "ip": "127.0.0.1",
        "phone": "18777976552",
        "email": "email@example.com",
        "id": 1234567,
        "name": "Xsolla User",
        "country": "US"
      }
    }'

using System;
using System.Security.Cryptography;
using System.Text;
public static class XsollaWebhookSignature
{
    public static string ComputeSha1(string jsonBody, string secretKey)
    {
        // Concatenation of the JSON from the request body and the project's secret key
        string dataToSign = jsonBody + secretKey;
        using (SHA1 sha1 = SHA1.Create())
        {
            byte[] hashBytes = sha1.ComputeHash(Encoding.UTF8.GetBytes(dataToSign));
            // Convert hash bytes to lowercase hexadecimal string
            var hexString = new StringBuilder(hashBytes.Length * 2);
            foreach (byte b in hashBytes)
            {
                hexString.Append(b.ToString("x2"));
            }
            return hexString.ToString();
        }
    }
    public static bool VerifySignature(string jsonBody, string secretKey, string receivedSignature)
    {
        string computedSignature = ComputeSha1(jsonBody, secretKey);
        string receivedSignatureLower = receivedSignature.ToLower();
        // Use constant-time comparison to prevent timing attacks
        return ConstantTimeEquals(computedSignature, receivedSignatureLower);
    }
    private static bool ConstantTimeEquals(string a, string b)
    {
        if (a.Length != b.Length)
        {
            return false;
        }
        int result = 0;
        for (int i = 0; i < a.Length; i++)
        {
            result |= a[i] ^ b[i];
        }
        return result == 0;
    }
}

// For .NET 5.0 and later, you can use the more concise Convert.ToHexString method:
using System;
using System.Security.Cryptography;
using System.Text;
public static class XsollaWebhookSignature
{
    public static string ComputeSha1(string jsonBody, string secretKey)
    {
        string dataToSign = jsonBody + secretKey;
        using var sha1 = SHA1.Create();
        byte[] hashBytes = sha1.ComputeHash(Encoding.UTF8.GetBytes(dataToSign));
        return Convert.ToHexString(hashBytes).ToLower();
    }
    public static bool VerifySignature(string jsonBody, string secretKey, string receivedSignature)
    {
        string computedSignature = ComputeSha1(jsonBody, secretKey);
        string receivedSignatureLower = receivedSignature.ToLower();
        // Use constant-time comparison to prevent timing attacks
        return ConstantTimeEquals(computedSignature, receivedSignatureLower);
    }
    private static bool ConstantTimeEquals(string a, string b)
    {
        if (a.Length != b.Length)
        {
            return false;
        }
        int result = 0;
        for (int i = 0; i < a.Length; i++)
        {
            result |= a[i] ^ b[i];
        }
        return result == 0;
    }
}

// For .NET 7.0+, you can use the built-in CryptographicOperations.FixedTimeEquals:
using System.Security.Cryptography;
public static bool VerifySignature(string jsonBody, string secretKey, string receivedSignature)
{
    string computedSignature = ComputeSha1(jsonBody, secretKey);
    byte[] computedBytes = Encoding.UTF8.GetBytes(computedSignature);
    byte[] receivedBytes = Encoding.UTF8.GetBytes(receivedSignature.ToLower());
    return CryptographicOperations.FixedTimeEquals(computedBytes, receivedBytes);
}

#include <string>
#include <sstream>
#include <iomanip>
#include <openssl/sha.h>
class XsollaWebhookSignature {
public:
    static std::string computeSha1(const std::string& jsonBody, const std::string& secretKey) {
        // Concatenation of the JSON from the request body and the project's secret key
        std::string dataToSign = jsonBody + secretKey;
        unsigned char digest[SHA_DIGEST_LENGTH];
        // Create SHA1 hash
        SHA1(reinterpret_cast<const unsigned char*>(dataToSign.c_str()),
             dataToSign.length(), digest);
        // Convert to lowercase hexadecimal string
        std::ostringstream hexStream;
        hexStream << std::hex << std::setfill('0');
        for (int i = 0; i < SHA_DIGEST_LENGTH; ++i) {
            hexStream << std::setw(2) << static_cast<unsigned int>(digest[i]);
        }
        return hexStream.str();
    }
    static bool verifySignature(const std::string& jsonBody, const std::string& secretKey, const std::string& receivedSignature) {
        std::string computedSignature = computeSha1(jsonBody, secretKey);
        // Timing-safe comparison
        if (computedSignature.length() != receivedSignature.length()) {
            return false;
        }
        volatile unsigned char result = 0;
        for (size_t i = 0; i < computedSignature.length(); ++i) {
            result |= (computedSignature[i] ^ receivedSignature[i]);
        }
        return result == 0;
    }
};

package main
import (
	"crypto/sha1"
    "crypto/subtle"
	"encoding/hex"
	"strings"
)
type XsollaWebhookSignature struct{}
func (x *XsollaWebhookSignature) ComputeSha1(jsonBody, secretKey string) string {
	// Concatenation of the JSON from the request body and the project's secret key
	dataToSign := jsonBody + secretKey
	// Create SHA1 hash
	h := sha1.New()
	h.Write([]byte(dataToSign))
	signature := h.Sum(nil)
	// Convert to lowercase hexadecimal string
	return strings.ToLower(hex.EncodeToString(signature))
}
func (x *XsollaWebhookSignature) VerifySignature(jsonBody, secretKey, receivedSignature string) bool {
	computedSignature := x.ComputeSha1(jsonBody, secretKey)
	receivedSignatureLower := strings.ToLower(receivedSignature)
	// Use constant time comparison to prevent timing attacks
	return subtle.ConstantTimeCompare([]byte(computedSignature), []byte(receivedSignatureLower)) == 1
}

<?php
class XsollaWebhookSignature
{
    /**
     * Compute SHA1 signature from webhook JSON body and secret key
     *
     * @param string $jsonBody The raw JSON body from webhook
     * @param string $secretKey The project's secret key
     * @return string The lowercase SHA1 signature
     */
    public static function computeSha1(string $jsonBody, string $secretKey): string
    {
        // Concatenation of the JSON from the request body and the project's secret key
        $dataToSign = $jsonBody . $secretKey;
        // Generate SHA1 signature
        $signature = sha1($dataToSign);
        return strtolower($signature);
    }
    /**
     * Verify webhook signature using timing-safe comparison
     *
     * @param string $jsonBody The raw JSON body from webhook
     * @param string $secretKey The project's secret key  
     * @param string $receivedSignature The signature from authorization header
     * @return bool True if signature is valid, false otherwise
     */
    public static function verifySignature(string $jsonBody, string $secretKey, string $receivedSignature): bool
    {
        $computedSignature = self::computeSha1($jsonBody, $secretKey);
        // Use hash_equals for timing-safe comparison
        return hash_equals($computedSignature, strtolower($receivedSignature));
    }
}
?>

const crypto = require('crypto');
class XsollaWebhookSignature {
    // IMPORTANT: jsonBody must be the raw JSON string exactly as received from Xsolla
    static computeSha1(jsonBody, secretKey) {
        // Concatenation of the JSON from the request body and the project's secret key
        const dataToSign = jsonBody + secretKey;
        // Create SHA1 hash
        const hash = crypto.createHash('sha1');
        hash.update(dataToSign, 'utf8');
        // Convert to lowercase hexadecimal string
        return hash.digest('hex').toLowerCase();
    }
    static verifySignature(jsonBody, secretKey, receivedSignature) {
        const computedSignature = this.computeSha1(jsonBody, secretKey);
        const cleanReceivedSignature = receivedSignature.toLowerCase();
        // Check if signatures have the same length before using timingSafeEqual
        if (computedSignature.length !== cleanReceivedSignature.length) {
            return false;
        }
        try {
            return crypto.timingSafeEqual(
                Buffer.from(computedSignature, 'hex'),
                Buffer.from(cleanReceivedSignature, 'hex')
            );
        } catch (error) {
            // Return false if there's any error (e.g., invalid hex characters)
            return false;
        }
    }
}

HTTP/1.1 400 Bad Request
{
    "error":{
        "code":"INVALID_USER",
        "message":"Invalid user"
    }
}

HTTP POST /webhooks/xsolla
  read raw_body, headers
  if !verify_signature(raw_body, headers['authorization']):
     return 400 {"error":{"code":"INVALID_SIGNATURE","message":"Invalid signature"}}
  enqueue(raw_body)
  return 204  # or 200