Verifying Genesys Cloud Webhook Payload Signatures in Go

What You Will Build

A production-ready Go HTTP server that receives Genesys Cloud webhooks, verifies HMAC-SHA256 payload signatures, enforces timestamp freshness windows, rotates secrets via the Architecture API, and exposes a management endpoint for automated verification status. The code uses the Genesys Cloud REST API directly, implements atomic secret validation, tracks latency and success rates, and generates structured audit logs for security governance.

Prerequisites

• Genesys Cloud OAuth client credentials with webhook:read and oauth:client:read scopes
• Go 1.21 or higher
• Standard library packages: net/http, crypto/hmac, crypto/sha256, encoding/hex, time, sync, log/slog, context, encoding/json
• Optional: github.com/prometheus/client_golang/prometheus for metrics exposure
• External vault service endpoint (AWS Secrets Manager, HashiCorp Vault, or Azure Key Vault)

Authentication Setup

Genesys Cloud uses OAuth 2.0 client credentials flow for server-to-server API access. The following code fetches an access token and caches it with automatic refresh logic. The token is required to query the Architecture API for webhook secrets.

package auth

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"sync"
	"time"
)

type TokenResponse struct {
	AccessToken string `json:"access_token"`
	ExpiresIn   int    `json:"expires_in"`
	TokenType   string `json:"token_type"`
}

type OAuthClient struct {
	environment string
	clientID    string
	clientSecret string
	token       *TokenResponse
	mu          sync.RWMutex
	httpClient  *http.Client
}

func NewOAuthClient(env, clientID, clientSecret string) *OAuthClient {
	return &OAuthClient{
		environment:  env,
		clientID:     clientID,
		clientSecret: clientSecret,
		httpClient:   &http.Client{Timeout: 10 * time.Second},
	}
}

func (o *OAuthClient) GetToken(ctx context.Context) (*TokenResponse, error) {
	o.mu.RLock()
	if o.token != nil && time.Since(o.token.issuedAt) < time.Duration(o.token.ExpiresIn-30)*time.Second {
		tok := o.token
		o.mu.RUnlock()
		return tok, nil
	}
	o.mu.RUnlock()

	o.mu.Lock()
	defer o.mu.Unlock()

	// Double-check after acquiring write lock
	if o.token != nil && time.Since(o.token.issuedAt) < time.Duration(o.token.ExpiresIn-30)*time.Second {
		return o.token, nil
	}

	url := fmt.Sprintf("https://%s.my.genesyscloud.com/oauth/token", o.environment)
	payload := fmt.Sprintf("client_id=%s&client_secret=%s&grant_type=client_credentials", o.clientID, o.clientSecret)
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewBufferString(payload))
	if err != nil {
		return nil, fmt.Errorf("failed to create token request: %w", err)
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

	resp, err := o.httpClient.Do(req)
	if err != nil {
		return nil, fmt.Errorf("token request failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(resp.Body)
		return nil, fmt.Errorf("oauth error %d: %s", resp.StatusCode, string(body))
	}

	var tok TokenResponse
	if err := json.NewDecoder(resp.Body).Decode(&tok); err != nil {
		return nil, fmt.Errorf("failed to decode token response: %w", err)
	}

	o.token = &tok
	o.token.issuedAt = time.Now()
	return o.token, nil
}

// issuedAt is not exported but tracked internally
type TokenResponse struct {
	AccessToken string    `json:"access_token"`
	ExpiresIn   int       `json:"expires_in"`
	TokenType   string    `json:"token_type"`
	issuedAt    time.Time // internal tracking
}

Implementation

Step 1: Fetch Webhook Secret via Architecture API

The Architecture API exposes webhook configuration at GET /api/v2/external/webhooks/{webhookId}. This endpoint returns the secret field used for HMAC verification. The call requires the webhook:read OAuth scope.

package genesys

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"time"
)

type WebhookConfig struct {
	ID     string `json:"id"`
	Secret string `json:"secret"`
	Status string `json:"status"`
}

func FetchWebhookSecret(ctx context.Context, env, webhookID, token string) (*WebhookConfig, error) {
	url := fmt.Sprintf("https://%s.my.genesyscloud.com/api/v2/external/webhooks/%s", env, webhookID)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, fmt.Errorf("request creation failed: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+token)
	req.Header.Set("Accept", "application/json")

	client := &http.Client{Timeout: 15 * time.Second}
	resp, err := client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("architecture api call failed: %w", err)
	}
	defer resp.Body.Close()

	switch resp.StatusCode {
	case http.StatusOK:
		var config WebhookConfig
		if err := json.NewDecoder(resp.Body).Decode(&config); err != nil {
			return nil, fmt.Errorf("json decode failed: %w", err)
		}
		return &config, nil
	case http.StatusUnauthorized, http.StatusForbidden:
		return nil, fmt.Errorf("authentication or authorization failed: %d", resp.StatusCode)
	case http.StatusTooManyRequests:
		return nil, fmt.Errorf("rate limited: %d", resp.StatusCode)
	default:
		body, _ := io.ReadAll(resp.Body)
		return nil, fmt.Errorf("api error %d: %s", resp.StatusCode, string(body))
	}
}

Step 2: Implement HMAC-SHA256 Verification and Timestamp Freshness

Genesys Cloud signs webhook payloads using HMAC-SHA256. The signature arrives in the X-Genesys-Signature header with a v1= prefix. The timestamp arrives in X-Genesys-Timestamp. This step validates both against a configurable freshness window to prevent replay attacks.

package verifier

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"strings"
	"time"
)

type VerificationResult struct {
	Valid       bool
	Reason      string
	LatencyMs   float64
	TimestampDrift time.Duration
}

func VerifyPayload(payload []byte, signatureHeader string, timestampHeader string, secret string, maxDrift time.Duration) *VerificationResult {
	start := time.Now()
	result := &VerificationResult{}

	// Parse signature header
	if !strings.HasPrefix(signatureHeader, "v1=") {
		result.Reason = "missing v1 prefix in signature header"
		return result
	}
	expectedSig := strings.TrimPrefix(signatureHeader, "v1=")

	// Calculate HMAC-SHA256
	mac := hmac.New(sha256.New, []byte(secret))
	mac.Write(payload)
	computedSig := hex.EncodeToString(mac.Sum(nil))

	if !hmac.Equal([]byte(expectedSig), []byte(computedSig)) {
		result.Reason = "signature mismatch"
		result.LatencyMs = time.Since(start).Seconds() * 1000
		return result
	}

	// Validate timestamp freshness
	if timestampHeader == "" {
		result.Reason = "missing timestamp header"
		result.LatencyMs = time.Since(start).Seconds() * 1000
		return result
	}

	webhookTime, err := time.Parse(time.RFC3339, timestampHeader)
	if err != nil {
		result.Reason = fmt.Sprintf("invalid timestamp format: %w", err)
		result.LatencyMs = time.Since(start).Seconds() * 1000
		return result
	}

	drift := time.Since(webhookTime)
	if drift < 0 {
		drift = -drift
	}
	result.TimestampDrift = drift

	if drift > maxDrift {
		result.Reason = fmt.Sprintf("timestamp drift %v exceeds maximum %v", drift, maxDrift)
		result.LatencyMs = time.Since(start).Seconds() * 1000
		return result
	}

	result.Valid = true
	result.LatencyMs = time.Since(start).Seconds() * 1000
	return result
}

Step 3: Secret Rotation and Vault Synchronization

Secret rotation requires fetching the latest secret from Genesys Cloud, comparing it against the cached value, and synchronizing the new value to an external vault. The following code implements atomic rotation with audit logging.

package rotation

import (
	"context"
	"fmt"
	"log/slog"
	"sync"
	"time"
)

type VaultClient interface {
	StoreSecret(ctx context.Context, name string, value string) error
}

type Rotator struct {
	currentSecret string
	mu            sync.RWMutex
	vault         VaultClient
	logger        *slog.Logger
	lastRotation  time.Time
}

func NewRotator(vault VaultClient, logger *slog.Logger) *Rotator {
	return &Rotator{
		vault:  vault,
		logger: logger,
	}
}

func (r *Rotator) CheckAndRotate(ctx context.Context, newSecret string) error {
	r.mu.Lock()
	defer r.mu.Unlock()

	if r.currentSecret == newSecret {
		return nil
	}

	if err := r.vault.StoreSecret(ctx, "genesys-webhook-secret", newSecret); err != nil {
		r.logger.Error("vault sync failed", "error", err)
		return fmt.Errorf("vault synchronization failed: %w", err)
	}

	r.currentSecret = newSecret
	r.lastRotation = time.Now()
	r.logger.Info("secret rotated successfully", "timestamp", r.lastRotation.Format(time.RFC3339))
	return nil
}

func (r *Rotator) GetSecret() string {
	r.mu.RLock()
	defer r.mu.RUnlock()
	return r.currentSecret
}

Step 4: Metrics, Audit Logging, and Management Endpoint

This step combines verification, rotation, metrics tracking, and exposes a REST endpoint for automated management. The handler tracks latency, success rates, and writes structured audit logs.

package server

import (
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"net/http"
	"sync/atomic"
	"time"

	"example.com/verifier"
	"example.com/rotation"
	"example.com/genesys"
	"example.com/auth"
)

type Metrics struct {
	TotalRequests   atomic.Int64
	ValidSignatures atomic.Int64
	InvalidSignatures atomic.Int64
	AvgLatencyMs    atomic.Float64
}

type WebhookServer struct {
	oauth      *auth.OAuthClient
	env        string
	webhookID  string
	rotator    *rotation.Rotator
	metrics    *Metrics
	logger     *slog.Logger
	maxDrift   time.Duration
}

func NewWebhookServer(oauth *auth.OAuthClient, env, webhookID string, rotator *rotation.Rotator, logger *slog.Logger) *WebhookServer {
	return &WebhookServer{
		oauth:     oauth,
		env:       env,
		webhookID: webhookID,
		rotator:   rotator,
		metrics:   &Metrics{},
		logger:    logger,
		maxDrift:  5 * time.Minute,
	}
}

func (s *WebhookServer) HandleWebhook(w http.ResponseWriter, r *http.Request) {
	start := time.Now()
	s.metrics.TotalRequests.Add(1)

	body, err := io.ReadAll(r.Body)
	if err != nil {
		http.Error(w, "failed to read body", http.StatusBadRequest)
		return
	}
	defer r.Body.Close()

	signature := r.Header.Get("X-Genesys-Signature")
	timestamp := r.Header.Get("X-Genesys-Timestamp")
	secret := s.rotator.GetSecret()

	result := verifier.VerifyPayload(body, signature, timestamp, secret, s.maxDrift)

	s.metrics.AvgLatencyMs.Add(result.LatencyMs)

	if result.Valid {
		s.metrics.ValidSignatures.Add(1)
		s.logger.Info("webhook verified", "drift", result.TimestampDrift, "latency_ms", result.LatencyMs)
		w.WriteHeader(http.StatusOK)
	} else {
		s.metrics.InvalidSignatures.Add(1)
		s.logger.Warn("webhook verification failed", "reason", result.Reason, "latency_ms", result.LatencyMs)
		w.WriteHeader(http.StatusUnauthorized)
	}
}

func (s *WebhookServer) HandleManagement(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}

	ctx, cancel := context.WithTimeout(r.Context(), 10*time.Second)
	defer cancel()

	token, err := s.oauth.GetToken(ctx)
	if err != nil {
		http.Error(w, fmt.Sprintf("token fetch failed: %v", err), http.StatusInternalServerError)
		return
	}

	config, err := genesys.FetchWebhookSecret(ctx, s.env, s.webhookID, token.AccessToken)
	if err != nil {
		http.Error(w, fmt.Sprintf("architecture api failed: %v", err), http.StatusBadGateway)
		return
	}

	if err := s.rotator.CheckAndRotate(ctx, config.Secret); err != nil {
		http.Error(w, fmt.Sprintf("rotation failed: %v", err), http.StatusInternalServerError)
		return
	}

	resp := map[string]interface{}{
		"status":             "active",
		"webhook_id":         config.ID,
		"secret_rotated":     s.rotator.GetSecret() == config.Secret,
		"total_requests":     s.metrics.TotalRequests.Load(),
		"valid_signatures":   s.metrics.ValidSignatures.Load(),
		"invalid_signatures": s.metrics.InvalidSignatures.Load(),
		"avg_latency_ms":     s.metrics.AvgLatencyMs.Load() / float64(max(1, s.metrics.TotalRequests.Load())),
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(resp)
}

func max(a, b int64) int64 {
	if a > b {
		return a
	}
	return b
}

Complete Working Example

The following file combines all components into a runnable server. Replace placeholder values with your Genesys Cloud environment details.

package main

import (
	"context"
	"log/slog"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

	"example.com/auth"
	"example.com/rotation"
	"example.com/server"
)

// Mock vault implementation for demonstration
type MockVault struct{}
func (m *MockVault) StoreSecret(ctx context.Context, name string, value string) error {
	slog.Info("vault store called", "name", name)
	return nil
}

func main() {
	logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
	logger.Info("starting webhook verifier service")

	environment := os.Getenv("GENESYS_ENV")
	if environment == "" {
		environment = "mypurecloud"
	}
	clientID := os.Getenv("GENESYS_CLIENT_ID")
	clientSecret := os.Getenv("GENESYS_CLIENT_SECRET")
	webhookID := os.Getenv("GENESYS_WEBHOOK_ID")

	if clientID == "" || clientSecret == "" || webhookID == "" {
		logger.Error("missing required environment variables")
		os.Exit(1)
	}

	oauth := auth.NewOAuthClient(environment, clientID, clientSecret)
	vault := &MockVault{}
	rotator := rotation.NewRotator(vault, logger)
	svc := server.NewWebhookServer(oauth, environment, webhookID, rotator, logger)

	mux := http.NewServeMux()
	mux.HandleFunc("/webhook/receive", svc.HandleWebhook)
	mux.HandleFunc("/management/status", svc.HandleManagement)

	srv := &http.Server{
		Addr:         ":8443",
		Handler:      mux,
		ReadTimeout:  15 * time.Second,
		WriteTimeout: 15 * time.Second,
		IdleTimeout:  60 * time.Second,
	}

	go func() {
		logger.Info("server listening", "addr", srv.Addr)
		if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
			logger.Error("server failed", "error", err)
			os.Exit(1)
		}
	}()

	quit := make(chan os.Signal, 1)
	signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
	<-quit

	logger.Info("shutting down server")
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	if err := srv.Shutdown(ctx); err != nil {
		logger.Error("shutdown failed", "error", err)
	}
	logger.Info("server stopped")
}

Common Errors and Debugging

Error: 401 Unauthorized on Architecture API

• Cause: Expired OAuth token or missing webhook:read scope on the client.
• Fix: Verify the OAuth client configuration in Genesys Cloud admin. Ensure the token cache refreshes before expiration. The provided OAuthClient includes a 30-second buffer.

Error: 429 Too Many Requests

• Cause: Exceeding Genesys Cloud rate limits (typically 100 requests per minute for Architecture API).
• Fix: Implement exponential backoff. The FetchWebhookSecret function returns the error; wrap it with a retry library like avast/retry-go with jitter.

Error: Signature Mismatch

• Cause: Payload modification during transit, incorrect secret, or missing v1= prefix handling.
• Fix: Log the raw payload and computed signature in debug mode. Ensure the secret matches the webhook configuration. Verify that the HTTP framework does not modify the body before verification.

Error: Timestamp Drift Exceeds Maximum

• Cause: Server clock skew or delayed event processing.
• Fix: Synchronize server time with NTP. Adjust maxDrift in WebhookServer if legitimate delays exist. The verification logic uses absolute value drift calculation.

Error: Vault Synchronization Failure

• Cause: Network timeout or IAM permissions missing on the external vault.
• Fix: Check vault endpoint connectivity and credentials. The CheckAndRotate method returns detailed errors. Implement retry logic with circuit breaker patterns for production vaults.

Official References

• Genesys Cloud OAuth 2.0 Documentation
• Architecture API Webhook Endpoint
• Webhook Security and Signature Verification
• Go Standard Library HTTP Package
• Go Crypto HMAC Package