Validate NICE CXone Caller ID Formats and Attestation Levels with Go

What You Will Build

• The code validates outbound caller ID formats against E.164 standards, verifies telephony constraints, and determines STIR/SHAKEN attestation levels before registering numbers in NICE CXone.
• This implementation uses the NICE CXone Voice API v2 endpoints for number capabilities and caller ID management.
• The tutorial covers Go 1.21 with the standard net/http library, structured validation pipelines, and automated webhook synchronization.

Prerequisites

• OAuth client type: Service Account or Machine-to-Machine (Client Credentials)
• Required scopes: voice:numbers:read, voice:caller-ids:read, voice:outbound-calls:write
• API version: NICE CXone REST API v2
• Language/runtime: Go 1.21 or later
• External dependencies: None. The standard library provides all necessary functionality for HTTP, JSON, regex, and concurrency control.

Authentication Setup

NICE CXone requires OAuth 2.0 client credentials flow for programmatic access. You must cache the access token and refresh it before expiration to avoid interrupting validation pipelines. The following code demonstrates a thread-safe token cache with automatic refresh logic.

package main

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

type OAuthConfig struct {
	BaseURL   string
	ClientID  string
	Secret    string
	GrantType string
}

type TokenResponse struct {
	AccessToken string `json:"access_token"`
	TokenType   string `json:"token_type"`
	ExpiresIn   int64  `json:"expires_in"`
}

type TokenCache struct {
	mu          sync.RWMutex
	token       string
	expiresAt   time.Time
	refreshFunc func(ctx context.Context) (string, error)
}

func NewTokenCache(cfg OAuthConfig) *TokenCache {
	return &TokenCache{
		refreshFunc: func(ctx context.Context) (string, error) {
			payload := fmt.Sprintf(
				"grant_type=%s&client_id=%s&client_secret=%s",
				cfg.GrantType, cfg.ClientID, cfg.Secret,
			)
			req, err := http.NewRequestWithContext(ctx, http.MethodPost, cfg.BaseURL+"/oauth/token", nil)
			if err != nil {
				return "", err
			}
			req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
			req.SetBasicAuth(cfg.ClientID, cfg.Secret)

			client := &http.Client{Timeout: 10 * time.Second}
			resp, err := client.Do(req)
			if err != nil {
				return "", err
			}
			defer resp.Body.Close()

			if resp.StatusCode != http.StatusOK {
				return "", fmt.Errorf("oauth error: status %d", resp.StatusCode)
			}

			var tr TokenResponse
			if err := json.NewDecoder(resp.Body).Decode(&tr); err != nil {
				return "", err
			}
			return tr.AccessToken, nil
		},
	}
}

func (tc *TokenCache) GetToken(ctx context.Context) (string, error) {
	tc.mu.RLock()
	if time.Now().Before(tc.expiresAt) {
		token := tc.token
		tc.mu.RUnlock()
		return token, nil
	}
	tc.mu.RUnlock()

	tc.mu.Lock()
	defer tc.mu.Unlock()
	if time.Now().Before(tc.expiresAt) {
		return tc.token, nil
	}

	token, err := tc.refreshFunc(ctx)
	if err != nil {
		return "", err
	}
	tc.token = token
	tc.expiresAt = time.Now().Add(55 * time.Minute)
	return token, nil
}

The OAuth endpoint requires the application/x-www-form-urlencoded content type. The token expires in one hour, but the cache refreshes at 55 minutes to prevent boundary failures. You must attach the token to every subsequent Voice API request using the Authorization: Bearer <token> header.

Implementation

Step 1: Configure the Validation Pipeline and Retry Logic

Telephony APIs enforce strict format constraints. You must validate digit counts, E.164 compliance, and STIR/SHAKEN attestation eligibility before submission. The Voice API returns HTTP 429 when rate limits are exceeded, so you must implement exponential backoff.

import (
	"crypto/rand"
	"math/big"
	"net/http"
	"time"
)

type ValidationConfig struct {
	MaxDigits        int
	E164Pattern      *regexp.Regexp
	AttestationRules map[string]string
}

func NewValidationConfig() *ValidationConfig {
	return &ValidationConfig{
		MaxDigits: 15,
		E164Pattern: regexp.MustCompile(`^\+?[1-9]\d{1,14}$`),
		AttestationRules: map[string]string{
			"owned":      "A",
			"ported":     "B",
			"third_party": "C",
			"toll_free":  "T",
		},
	}
}

func DoWithRetry(ctx context.Context, method, url string, headers map[string]string, body []byte, maxRetries int) (*http.Response, error) {
	client := &http.Client{Timeout: 15 * time.Second}
	var lastErr error

	for attempt := 0; attempt <= maxRetries; attempt++ {
		req, err := http.NewRequestWithContext(ctx, method, url, nil)
		if body != nil {
			req.Body = http.NoBody
			req.GetBody = func() (io.ReadCloser, error) {
				return io.NopCloser(bytes.NewReader(body)), nil
			}
		}
		for k, v := range headers {
			req.Header.Set(k, v)
		}

		resp, err := client.Do(req)
		if err != nil {
			lastErr = err
			continue
		}

		if resp.StatusCode == http.StatusTooManyRequests {
			delay, _ := time.ParseDuration(resp.Header.Get("Retry-After"))
			if delay == 0 {
				delay = time.Duration(attempt+1) * 2 * time.Second
			}
			resp.Body.Close()
			time.Sleep(delay)
			continue
		}

		if resp.StatusCode >= http.StatusInternalServerError {
			resp.Body.Close()
			lastErr = fmt.Errorf("server error: %d", resp.StatusCode)
			time.Sleep(time.Duration(attempt+1) * time.Second)
			continue
		}

		return resp, nil
	}
	return nil, lastErr
}

The retry logic respects the Retry-After header returned by CXone. If the header is absent, it falls back to exponential backoff. You must close the response body on every failed attempt to prevent connection pool exhaustion.

Step 2: Normalize Numbers and Query Voice API Capabilities

You must normalize caller IDs to E.164 format and verify portability status through the Voice API. The /api/v2/voice/numbers endpoint returns number capabilities including attestation eligibility and CNAM registration status.

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

type NumberCapability struct {
	ID            string `json:"id"`
	Number        string `json:"number"`
	Status        string `json:"status"`
	CNAMStatus    string `json:"cnam_status"`
	Attestation   string `json:"attestation_level"`
	Ported        bool   `json:"ported"`
	TollFree      bool   `json:"toll_free"`
}

type ValidationMetrics struct {
	mu          sync.Mutex
	TotalChecks int64
	Successes   int64
	LastLatency time.Duration
}

func (vm *ValidationMetrics) Record(duration time.Duration, success bool) {
	vm.mu.Lock()
	defer vm.mu.Unlock()
	vm.TotalChecks++
	vm.LastLatency = duration
	if success {
		vm.Successes++
	}
}

func ValidateCallerID(ctx context.Context, cache *TokenCache, cfg *ValidationConfig, number string) (*NumberCapability, error) {
	start := time.Now()
	token, err := cache.GetToken(ctx)
	if err != nil {
		return nil, fmt.Errorf("authentication failed: %w", err)
	}

	normalized := strings.TrimLeft(number, "+")
	if !cfg.E164Pattern.MatchString("+"+normalized) {
		return nil, fmt.Errorf("invalid e.164 format: %s", number)
	}
	if len(normalized) > cfg.MaxDigits {
		return nil, fmt.Errorf("exceeds maximum digit count of %d", cfg.MaxDigits)
	}

	headers := map[string]string{
		"Authorization": "Bearer " + token,
		"Accept":        "application/json",
		"Content-Type":  "application/json",
	}

	url := fmt.Sprintf("%s/api/v2/voice/numbers?search=%s&page=1&pageSize=1", "https://api.cxone.com", normalized)
	resp, err := DoWithRetry(ctx, http.MethodGet, url, headers, nil, 3)
	if err != nil {
		return nil, fmt.Errorf("api request failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode == http.StatusUnauthorized {
		cache.mu.Lock()
		cache.token = ""
		cache.expiresAt = time.Time{}
		cache.mu.Unlock()
		return nil, fmt.Errorf("token expired, refresh required")
	}
	if resp.StatusCode == http.StatusForbidden {
		return nil, fmt.Errorf("insufficient scopes: requires voice:numbers:read")
	}

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, err
	}

	var result struct {
		Entity []NumberCapability `json:"entity"`
	}
	if err := json.Unmarshal(body, &result); err != nil {
		return nil, err
	}

	if len(result.Entity) == 0 {
		return nil, fmt.Errorf("number not found in cxone inventory")
	}

	cap := result.Entity[0]
	success := true
	if cap.CNAMStatus != "registered" && cap.CNAMStatus != "pending" {
		success = false
	}
	cfg.AttestationRules["actual"] = cap.Attestation
	vm := &ValidationMetrics{}
	vm.Record(time.Since(start), success)

	return &cap, nil
}

The GET request uses query parameters for pagination and search. You must handle the entity array because CXone returns a wrapper object. The code checks cnam_status and attestation_level directly from the response. If the number lacks CNAM registration, the pipeline flags it for remediation before outbound routing.

Step 3: Webhook Synchronization, Audit Logging, and Fraud Detection

You must synchronize validation events with external fraud detection systems and generate governance audit logs. The following code constructs a webhook payload, tracks success rates, and outputs structured logs.

import (
	"bytes"
	"encoding/json"
	"fmt"
	"log"
	"time"
)

type WebhookPayload struct {
	Event     string           `json:"event"`
	Timestamp time.Time        `json:"timestamp"`
	Number    string           `json:"number"`
	Status    string           `json:"status"`
	Attestation string         `json:"attestation"`
	Metrics   ValidationMetrics `json:"metrics"`
}

func SendValidationWebhook(ctx context.Context, webhookURL string, cap *NumberCapability, vm *ValidationMetrics) error {
	payload := WebhookPayload{
		Event:     "caller_id_validated",
		Timestamp: time.Now().UTC(),
		Number:    cap.Number,
		Status:    cap.Status,
		Attestation: cap.Attestation,
		Metrics:   *vm,
	}

	jsonBody, err := json.Marshal(payload)
	if err != nil {
		return err
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, webhookURL, bytes.NewReader(jsonBody))
	if err != nil {
		return err
	}
	req.Header.Set("Content-Type", "application/json")

	client := &http.Client{Timeout: 5 * time.Second}
	resp, err := client.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return fmt.Errorf("webhook delivery failed: %d", resp.StatusCode)
	}
	return nil
}

func GenerateAuditLog(cap *NumberCapability, success bool, duration time.Duration) {
	log.Printf(
		`{"event":"caller_id_audit","number":"%s","status":"%s","attestation":"%s","success":%t,"latency_ms":%d,"timestamp":"%s"}`,
		cap.Number, cap.Status, cap.Attestation, success, duration.Milliseconds(), time.Now().UTC().Format(time.RFC3339),
	)
}

The webhook payload includes the attestation level and validation metrics. You must marshal the payload to JSON and set the Content-Type header explicitly. The audit log outputs machine-readable JSON to stdout, which you can pipe to a centralized logging system. The success flag reflects CNAM registration and attestation eligibility.

Complete Working Example

The following script combines authentication, validation, webhook synchronization, and metrics tracking into a single executable program. Replace the placeholder credentials before execution.

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"regexp"
	"strings"
	"sync"
	"time"
)

type OAuthConfig struct {
	BaseURL   string
	ClientID  string
	Secret    string
	GrantType string
}

type TokenResponse struct {
	AccessToken string `json:"access_token"`
	ExpiresIn   int64  `json:"expires_in"`
}

type TokenCache struct {
	mu          sync.RWMutex
	token       string
	expiresAt   time.Time
	refreshFunc func(ctx context.Context) (string, error)
}

func NewTokenCache(cfg OAuthConfig) *TokenCache {
	return &TokenCache{
		refreshFunc: func(ctx context.Context) (string, error) {
			payload := fmt.Sprintf(
				"grant_type=%s&client_id=%s&client_secret=%s",
				cfg.GrantType, cfg.ClientID, cfg.Secret,
			)
			req, err := http.NewRequestWithContext(ctx, http.MethodPost, cfg.BaseURL+"/oauth/token", strings.NewReader(payload))
			if err != nil {
				return "", err
			}
			req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

			client := &http.Client{Timeout: 10 * time.Second}
			resp, err := client.Do(req)
			if err != nil {
				return "", err
			}
			defer resp.Body.Close()

			if resp.StatusCode != http.StatusOK {
				return "", fmt.Errorf("oauth error: status %d", resp.StatusCode)
			}

			var tr TokenResponse
			if err := json.NewDecoder(resp.Body).Decode(&tr); err != nil {
				return "", err
			}
			return tr.AccessToken, nil
		},
	}
}

func (tc *TokenCache) GetToken(ctx context.Context) (string, error) {
	tc.mu.RLock()
	if time.Now().Before(tc.expiresAt) {
		token := tc.token
		tc.mu.RUnlock()
		return token, nil
	}
	tc.mu.RUnlock()

	tc.mu.Lock()
	defer tc.mu.Unlock()
	if time.Now().Before(tc.expiresAt) {
		return tc.token, nil
	}

	token, err := tc.refreshFunc(ctx)
	if err != nil {
		return "", err
	}
	tc.token = token
	tc.expiresAt = time.Now().Add(55 * time.Minute)
	return token, nil
}

type ValidationConfig struct {
	MaxDigits        int
	E164Pattern      *regexp.Regexp
	AttestationRules map[string]string
}

func NewValidationConfig() *ValidationConfig {
	return &ValidationConfig{
		MaxDigits: 15,
		E164Pattern: regexp.MustCompile(`^\+?[1-9]\d{1,14}$`),
		AttestationRules: map[string]string{
			"owned":      "A",
			"ported":     "B",
			"third_party": "C",
			"toll_free":  "T",
		},
	}
}

type NumberCapability struct {
	ID            string `json:"id"`
	Number        string `json:"number"`
	Status        string `json:"status"`
	CNAMStatus    string `json:"cnam_status"`
	Attestation   string `json:"attestation_level"`
	Ported        bool   `json:"ported"`
	TollFree      bool   `json:"toll_free"`
}

type ValidationMetrics struct {
	mu          sync.Mutex
	TotalChecks int64
	Successes   int64
	LastLatency time.Duration
}

func (vm *ValidationMetrics) Record(duration time.Duration, success bool) {
	vm.mu.Lock()
	defer vm.mu.Unlock()
	vm.TotalChecks++
	vm.LastLatency = duration
	if success {
		vm.Successes++
	}
}

func DoWithRetry(ctx context.Context, method, url string, headers map[string]string, maxRetries int) (*http.Response, error) {
	client := &http.Client{Timeout: 15 * time.Second}
	var lastErr error

	for attempt := 0; attempt <= maxRetries; attempt++ {
		req, err := http.NewRequestWithContext(ctx, method, url, nil)
		if err != nil {
			lastErr = err
			continue
		}
		for k, v := range headers {
			req.Header.Set(k, v)
		}

		resp, err := client.Do(req)
		if err != nil {
			lastErr = err
			continue
		}

		if resp.StatusCode == http.StatusTooManyRequests {
			delay, _ := time.ParseDuration(resp.Header.Get("Retry-After"))
			if delay == 0 {
				delay = time.Duration(attempt+1) * 2 * time.Second
			}
			resp.Body.Close()
			time.Sleep(delay)
			continue
		}

		if resp.StatusCode >= http.StatusInternalServerError {
			resp.Body.Close()
			lastErr = fmt.Errorf("server error: %d", resp.StatusCode)
			time.Sleep(time.Duration(attempt+1) * time.Second)
			continue
		}

		return resp, nil
	}
	return nil, lastErr
}

func ValidateCallerID(ctx context.Context, cache *TokenCache, cfg *ValidationConfig, number string) (*NumberCapability, *ValidationMetrics, error) {
	start := time.Now()
	token, err := cache.GetToken(ctx)
	if err != nil {
		return nil, nil, fmt.Errorf("authentication failed: %w", err)
	}

	normalized := strings.TrimLeft(number, "+")
	if !cfg.E164Pattern.MatchString("+"+normalized) {
		return nil, nil, fmt.Errorf("invalid e.164 format: %s", number)
	}
	if len(normalized) > cfg.MaxDigits {
		return nil, nil, fmt.Errorf("exceeds maximum digit count of %d", cfg.MaxDigits)
	}

	headers := map[string]string{
		"Authorization": "Bearer " + token,
		"Accept":        "application/json",
	}

	url := fmt.Sprintf("https://api.cxone.com/api/v2/voice/numbers?search=%s&page=1&pageSize=1", normalized)
	resp, err := DoWithRetry(ctx, http.MethodGet, url, headers, 3)
	if err != nil {
		return nil, nil, fmt.Errorf("api request failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode == http.StatusUnauthorized {
		cache.mu.Lock()
		cache.token = ""
		cache.expiresAt = time.Time{}
		cache.mu.Unlock()
		return nil, nil, fmt.Errorf("token expired, refresh required")
	}
	if resp.StatusCode == http.StatusForbidden {
		return nil, nil, fmt.Errorf("insufficient scopes: requires voice:numbers:read")
	}

	var result struct {
		Entity []NumberCapability `json:"entity"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
		return nil, nil, err
	}

	if len(result.Entity) == 0 {
		return nil, nil, fmt.Errorf("number not found in cxone inventory")
	}

	cap := result.Entity[0]
	vm := &ValidationMetrics{}
	success := cap.CNAMStatus == "registered" || cap.CNAMStatus == "pending"
	vm.Record(time.Since(start), success)

	return &cap, vm, nil
}

func SendValidationWebhook(ctx context.Context, webhookURL string, cap *NumberCapability, vm *ValidationMetrics) error {
	payload := map[string]interface{}{
		"event":       "caller_id_validated",
		"timestamp":   time.Now().UTC(),
		"number":      cap.Number,
		"status":      cap.Status,
		"attestation": cap.Attestation,
		"metrics": map[string]interface{}{
			"total_checks": vm.TotalChecks,
			"successes":    vm.Successes,
			"latency_ms":   vm.LastLatency.Milliseconds(),
		},
	}

	jsonBody, err := json.Marshal(payload)
	if err != nil {
		return err
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, webhookURL, nil)
	if err != nil {
		return err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Body = http.NoBody

	client := &http.Client{Timeout: 5 * time.Second}
	resp, err := client.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return fmt.Errorf("webhook delivery failed: %d", resp.StatusCode)
	}
	return nil
}

func main() {
	ctx := context.Background()

	cfg := OAuthConfig{
		BaseURL:   "https://api.cxone.com",
		ClientID:  "YOUR_CLIENT_ID",
		Secret:    "YOUR_CLIENT_SECRET",
		GrantType: "client_credentials",
	}

	cache := NewTokenCache(cfg)
	valCfg := NewValidationConfig()

	numberToValidate := "+14155552671"
	webhookURL := "https://your-fraud-system.com/api/v1/events"

	cap, metrics, err := ValidateCallerID(ctx, cache, valCfg, numberToValidate)
	if err != nil {
		log.Fatalf("validation failed: %v", err)
	}

	log.Printf("Validated number: %s | Attestation: %s | CNAM: %s", cap.Number, cap.Attestation, cap.CNAMStatus)

	if err := SendValidationWebhook(ctx, webhookURL, cap, metrics); err != nil {
		log.Printf("webhook sync warning: %v", err)
	}

	log.Printf(
		`{"event":"caller_id_audit","number":"%s","status":"%s","attestation":"%s","success":true,"latency_ms":%d,"timestamp":"%s"}`,
		cap.Number, cap.Status, cap.Attestation, metrics.LastLatency.Milliseconds(), time.Now().UTC().Format(time.RFC3339),
	)
}

Common Errors & Debugging

Error: 401 Unauthorized

• What causes it: The OAuth token expired during the validation window or the client credentials are invalid.
• How to fix it: Clear the token cache and trigger a refresh. Verify the client_id and client_secret match a service account with active status.
• Code showing the fix: The GetToken method resets expiresAt to zero when a 401 response is detected, forcing immediate refresh on the next call.

Error: 403 Forbidden

• What causes it: The OAuth token lacks the required voice:numbers:read scope.
• How to fix it: Regenerate the OAuth client token with the correct scope grants in the CXone admin console.
• Code showing the fix: The validation function explicitly checks for 403 and returns a descriptive error string that references the missing scope.

Error: 429 Too Many Requests

• What causes it: The validation pipeline exceeds CXone rate limits for number capability queries.
• How to fix it: Implement exponential backoff and respect the Retry-After header.
• Code showing the fix: The DoWithRetry function parses Retry-After and applies a fallback delay of (attempt+1) * 2 seconds before retrying.

Error: Number Not Found in Inventory

• What causes it: The caller ID has not been provisioned in CXone or belongs to a different organization.
• How to fix it: Provision the number through the Voice API or verify ownership in the CXone number management portal.
• Code showing the fix: The decoder checks len(result.Entity) == 0 and returns a structured error before proceeding to attestation logic.

Official References

• NICE CXone Voice Numbers API
• NICE CXone OAuth 2.0 Client Credentials Flow
• STIR/SHAKEN Attestation Levels Documentation
• NICE CXone Rate Limiting Guidelines