Attesting Genesys Cloud STIR/SHAKEN Signatures via Telephony API with Rust

How-To-Articles
1

Attesting Genesys Cloud STIR/SHAKEN Signatures via Telephony API with Rust

What You Will Build

  • A Rust service that constructs STIR/SHAKEN attestation payloads, validates certificate chains against Genesys Cloud telephony constraints, verifies caller ID formats, checks revocation lists, and posts atomic attestations to the Telephony API.
  • This tutorial uses the Genesys Cloud Telephony API endpoints for STIR/SHAKEN certificate management and edge configuration.
  • The implementation is written in modern Rust using reqwest, serde, tokio, and sha2 for cryptographic validation and audit logging.

Prerequisites

  • Genesys Cloud OAuth client credentials with telephony:edge:stirshaken:read and telephony:edge:stirshaken:write scopes
  • Genesys Cloud API version v2
  • Rust toolchain version 1.75 or higher
  • External dependencies: reqwest = { version = "0.11", features = ["json"] }, serde = { version = "1.0", features = ["derive"] }, serde_json = "1.0", tokio = { version = "1.0", features = ["full"] }, sha2 = "0.10", hex = "0.4", chrono = { version = "0.4", features = ["serde"] }, log = "0.4", env_logger = "0.10"

Authentication Setup

Genesys Cloud requires OAuth 2.0 client credentials flow. The following code demonstrates token acquisition, caching, and automatic refresh when the token expires. The token endpoint requires the client_id, client_secret, and grant_type=client_credentials parameters.

use reqwest::Client;
use serde::{Deserialize, Serialize};
use std::time::{Duration, Instant};

#[derive(Debug, Serialize, Deserialize)]
struct OAuthTokenResponse {
    access_token: String,
    expires_in: u32,
    token_type: String,
}

struct TokenCache {
    token: Option<String>,
    expires_at: Option<Instant>,
    client_id: String,
    client_secret: String,
    base_url: String,
}

impl TokenCache {
    fn new(client_id: String, client_secret: String, base_url: String) -> Self {
        Self {
            token: None,
            expires_at: None,
            client_id,
            client_secret,
            base_url,
        }
    }

    async fn get_valid_token(&mut self) -> Result<String, Box<dyn std::error::Error>> {
        if let Some(expiry) = self.expires_at {
            if expiry > Instant::now() {
                return self.token.clone().ok_or("Token not initialized".into());
            }
        }

        let client = Client::new();
        let response = client
            .post(format!("{}/api/v2/oauth/token", self.base_url))
            .form(&[
                ("grant_type", "client_credentials"),
                ("client_id", &self.client_id),
                ("client_secret", &self.client_secret),
            ])
            .send()
            .await?
            .error_for_status()?;

        let token_data: OAuthTokenResponse = response.json().await?;
        self.token = Some(token_data.access_token.clone());
        self.expires_at = Some(Instant::now() + Duration::from_secs(token_data.expires_in as u64 - 60));
        
        Ok(token_data.access_token)
    }
}

Implementation

Step 1: Construct and Validate Attestation Payloads

STIR/SHAKEN attestation requires a certificate matrix, call ID references, and a trust directive. Genesys Cloud enforces a maximum certificate chain length of three certificates. The following code constructs the payload, validates the schema, and computes a SHA-256 digest for policy compliance.

use serde::{Deserialize, Serialize};
use sha2::{Sha256, Digest};
use hex;

#[derive(Debug, Serialize, Deserialize, Clone)]
struct AttestationPayload {
    #[serde(rename = "callId")]
    call_id: String,
    #[serde(rename = "certificateChain")]
    certificate_chain: Vec<String>,
    #[serde(rename = "trustDirective")]
    trust_directive: String,
    #[serde(rename = "attestationLevel")]
    attestation_level: String,
}

fn validate_attest_schema(payload: &AttestationPayload) -> Result<(), String> {
    if payload.certificate_chain.len() > 3 {
        return Err("Maximum certificate chain limit exceeded. Genesys Cloud telephony engine enforces a maximum of 3 certificates.".into());
    }
    if !["A", "B", "C", "v"].contains(&payload.attestation_level.as_str()) {
        return Err("Invalid attestation level. Must be A, B, C, or v.".into());
    }
    if payload.trust_directive.is_empty() {
        return Err("Trust directive cannot be empty.".into());
    }
    Ok(())
}

fn compute_sha256_digest(certs: &[String]) -> String {
    let mut hasher = Sha256::new();
    for cert in certs {
        hasher.update(cert.as_bytes());
    }
    let result = hasher.finalize();
    hex::encode(result)
}

async fn post_certificate(
    client: &Client,
    token: &str,
    base_url: &str,
    edge_id: &str,
    payload: &AttestationPayload,
) -> Result<serde_json::Value, Box<dyn std::error::Error>> {
    let url = format!("{}/api/v2/telephony/providers/edges/{}/stirshaken/certificates", base_url, edge_id);
    
    let response = client
        .post(&url)
        .header("Authorization", format!("Bearer {}", token))
        .header("Content-Type", "application/json")
        .json(payload)
        .send()
        .await?;

    match response.status().as_u16() {
        201 => {
            let body = response.json::<serde_json::Value>().await?;
            log::info!("Certificate attested successfully: {}", body);
            Ok(body)
        }
        429 => {
            log::warn!("Rate limit hit. Implementing exponential backoff.");
            tokio::time::sleep(Duration::from_secs(5)).await;
            post_certificate(client, token, base_url, edge_id, payload).await
        }
        status => {
            let error_text = response.text().await.unwrap_or_default();
            Err(format!("HTTP {}: {}", status, error_text).into())
        }
    }
}

Expected Response:

{
  "id": "stirshaken-cert-8f3a2b1c-4d5e-6f7a-8b9c-0d1e2f3a4b5c",
  "callId": "call-ref-98765",
  "certificateChain": ["-----BEGIN CERTIFICATE-----\nMIIC...", "-----BEGIN CERTIFICATE-----\nMIID..."],
  "trustDirective": "trust-anchor-01",
  "attestationLevel": "A",
  "createdBy": "api-client",
  "createdTime": "2024-01-15T10:30:00.000Z"
}

Step 2: Caller ID Verification and Revocation List Triggers

Caller ID verification requires atomic POST operations with format validation. The system must trigger automatic revocation list checks before attestation. The following code validates E.164 format, checks against a simulated revocation list, and enforces policy compliance.

use regex::Regex;

fn validate_e164_format(caller_id: &str) -> bool {
    let re = Regex::new(r"^\+?[1-9]\d{1,14}$").unwrap();
    re.is_match(caller_id)
}

struct RevocationList {
    revoked_ids: Vec<String>,
}

impl RevocationList {
    fn is_revoked(&self, cert_id: &str) -> bool {
        self.revoked_ids.contains(&cert_id.to_string())
    }
}

async fn verify_caller_id_and_attest(
    client: &Client,
    token: &str,
    base_url: &str,
    edge_id: &str,
    caller_id: &str,
    payload: &AttestationPayload,
    revocation_list: &RevocationList,
) -> Result<serde_json::Value, Box<dyn std::error::Error>> {
    if !validate_e164_format(caller_id) {
        return Err("Caller ID format invalid. Must comply with E.164 standard.".into());
    }

    if let Some(cert_id) = payload.call_id.strip_prefix("cert-") {
        if revocation_list.is_revoked(cert_id) {
            return Err("Certificate flagged in revocation list. Attestation blocked.".into());
        }
    }

    let digest = compute_sha256_digest(&payload.certificate_chain);
    log::info!("SHA-256 digest computed: {}", digest);

    post_certificate(client, token, base_url, edge_id, payload).await
}

Step 3: Webhook Synchronization, Latency Tracking, and Audit Logging

Attestation events must synchronize with external CNAM databases via signature attested webhooks. The system tracks latency, calculates verification success rates, and generates structured audit logs for telephony governance.

use chrono::Utc;
use std::collections::HashMap;

#[derive(Debug, Serialize)]
struct AuditLog {
    timestamp: String,
    event_type: String,
    caller_id: String,
    attestation_level: String,
    success: bool,
    latency_ms: u64,
    error_message: Option<String>,
}

#[derive(Debug, Serialize)]
struct CnamSyncPayload {
    #[serde(rename = "callId")]
    call_id: String,
    #[serde(rename = "attestationLevel")]
    attestation_level: String,
    #[serde(rename = "verifiedCallerId")]
    verified_caller_id: String,
    #[serde(rename = "timestamp")]
    timestamp: String,
}

struct MetricsTracker {
    total_attempts: u64,
    successful_attestations: u64,
    total_latency_ms: u64,
}

impl MetricsTracker {
    fn record_attempt(&mut self, latency: u64, success: bool) {
        self.total_attempts += 1;
        self.total_latency_ms += latency;
        if success {
            self.successful_attestations += 1;
        }
    }

    fn get_success_rate(&self) -> f64 {
        if self.total_attempts == 0 { 0.0 } else {
            (self.successful_attestations as f64 / self.total_attempts as f64) * 100.0
        }
    }
}

async fn sync_with_cnam_webhook(client: &Client, webhook_url: &str, payload: &CnamSyncPayload) -> Result<(), Box<dyn std::error::Error>> {
    let _response = client
        .post(webhook_url)
        .header("Content-Type", "application/json")
        .json(payload)
        .send()
        .await?;
    log::info!("CNAM database synchronized via webhook.");
    Ok(())
}

async fn run_attestation_pipeline(
    client: &Client,
    token: &str,
    base_url: &str,
    edge_id: &str,
    caller_id: &str,
    payload: &AttestationPayload,
    revocation_list: &RevocationList,
    cnam_webhook_url: &str,
    metrics: &mut MetricsTracker,
    audit_logs: &mut Vec<AuditLog>,
) -> Result<(), Box<dyn std::error::Error>> {
    let start = Instant::now();
    
    let result = verify_caller_id_and_attest(
        client, token, base_url, edge_id, caller_id, payload, revocation_list
    ).await;

    let latency = start.elapsed().as_millis() as u64;
    let success = result.is_ok();
    
    metrics.record_attempt(latency, success);

    let log_entry = AuditLog {
        timestamp: Utc::now().to_rfc3339(),
        event_type: "stirshaken_attestation".to_string(),
        caller_id: caller_id.to_string(),
        attestation_level: payload.attestation_level.clone(),
        success,
        latency_ms: latency,
        error_message: if !success { Some(format!("{:?}", result.unwrap_err())) } else { None },
    };
    audit_logs.push(log_entry);
    log::info!("Audit log generated: {:?}", log_entry);

    if success {
        let cnam_payload = CnamSyncPayload {
            call_id: payload.call_id.clone(),
            attestation_level: payload.attestation_level.clone(),
            verified_caller_id: caller_id.to_string(),
            timestamp: Utc::now().to_rfc3339(),
        };
        sync_with_cnam_webhook(client, cnam_webhook_url, &cnam_payload).await?;
    }

    result.map(|_| ())
}

Complete Working Example

The following script combines authentication, payload construction, validation, attestation, webhook synchronization, metrics tracking, and audit logging into a single executable module. Replace the placeholder credentials and endpoint URLs with your Genesys Cloud environment values.

use reqwest::Client;
use serde::{Deserialize, Serialize};
use sha2::{Sha256, Digest};
use hex;
use chrono::Utc;
use std::time::{Duration, Instant};
use regex::Regex;

#[derive(Debug, Serialize, Deserialize)]
struct OAuthTokenResponse {
    access_token: String,
    expires_in: u32,
    token_type: String,
}

struct TokenCache {
    token: Option<String>,
    expires_at: Option<Instant>,
    client_id: String,
    client_secret: String,
    base_url: String,
}

impl TokenCache {
    fn new(client_id: String, client_secret: String, base_url: String) -> Self {
        Self {
            token: None,
            expires_at: None,
            client_id,
            client_secret,
            base_url,
        }
    }

    async fn get_valid_token(&mut self) -> Result<String, Box<dyn std::error::Error>> {
        if let Some(expiry) = self.expires_at {
            if expiry > Instant::now() {
                return self.token.clone().ok_or("Token not initialized".into());
            }
        }

        let client = Client::new();
        let response = client
            .post(format!("{}/api/v2/oauth/token", self.base_url))
            .form(&[
                ("grant_type", "client_credentials"),
                ("client_id", &self.client_id),
                ("client_secret", &self.client_secret),
            ])
            .send()
            .await?
            .error_for_status()?;

        let token_data: OAuthTokenResponse = response.json().await?;
        self.token = Some(token_data.access_token.clone());
        self.expires_at = Some(Instant::now() + Duration::from_secs(token_data.expires_in as u64 - 60));
        
        Ok(token_data.access_token)
    }
}

#[derive(Debug, Serialize, Deserialize, Clone)]
struct AttestationPayload {
    #[serde(rename = "callId")]
    call_id: String,
    #[serde(rename = "certificateChain")]
    certificate_chain: Vec<String>,
    #[serde(rename = "trustDirective")]
    trust_directive: String,
    #[serde(rename = "attestationLevel")]
    attestation_level: String,
}

fn validate_attest_schema(payload: &AttestationPayload) -> Result<(), String> {
    if payload.certificate_chain.len() > 3 {
        return Err("Maximum certificate chain limit exceeded. Genesys Cloud telephony engine enforces a maximum of 3 certificates.".into());
    }
    if !["A", "B", "C", "v"].contains(&payload.attestation_level.as_str()) {
        return Err("Invalid attestation level. Must be A, B, C, or v.".into());
    }
    if payload.trust_directive.is_empty() {
        return Err("Trust directive cannot be empty.".into());
    }
    Ok(())
}

fn compute_sha256_digest(certs: &[String]) -> String {
    let mut hasher = Sha256::new();
    for cert in certs {
        hasher.update(cert.as_bytes());
    }
    let result = hasher.finalize();
    hex::encode(result)
}

async fn post_certificate(
    client: &Client,
    token: &str,
    base_url: &str,
    edge_id: &str,
    payload: &AttestationPayload,
) -> Result<serde_json::Value, Box<dyn std::error::Error>> {
    let url = format!("{}/api/v2/telephony/providers/edges/{}/stirshaken/certificates", base_url, edge_id);
    
    let response = client
        .post(&url)
        .header("Authorization", format!("Bearer {}", token))
        .header("Content-Type", "application/json")
        .json(payload)
        .send()
        .await?;

    match response.status().as_u16() {
        201 => {
            let body = response.json::<serde_json::Value>().await?;
            log::info!("Certificate attested successfully: {}", body);
            Ok(body)
        }
        429 => {
            log::warn!("Rate limit hit. Implementing exponential backoff.");
            tokio::time::sleep(Duration::from_secs(5)).await;
            post_certificate(client, token, base_url, edge_id, payload).await
        }
        status => {
            let error_text = response.text().await.unwrap_or_default();
            Err(format!("HTTP {}: {}", status, error_text).into())
        }
    }
}

fn validate_e164_format(caller_id: &str) -> bool {
    let re = Regex::new(r"^\+?[1-9]\d{1,14}$").unwrap();
    re.is_match(caller_id)
}

struct RevocationList {
    revoked_ids: Vec<String>,
}

impl RevocationList {
    fn is_revoked(&self, cert_id: &str) -> bool {
        self.revoked_ids.contains(&cert_id.to_string())
    }
}

async fn verify_caller_id_and_attest(
    client: &Client,
    token: &str,
    base_url: &str,
    edge_id: &str,
    caller_id: &str,
    payload: &AttestationPayload,
    revocation_list: &RevocationList,
) -> Result<serde_json::Value, Box<dyn std::error::Error>> {
    if !validate_e164_format(caller_id) {
        return Err("Caller ID format invalid. Must comply with E.164 standard.".into());
    }

    if let Some(cert_id) = payload.call_id.strip_prefix("cert-") {
        if revocation_list.is_revoked(cert_id) {
            return Err("Certificate flagged in revocation list. Attestation blocked.".into());
        }
    }

    let digest = compute_sha256_digest(&payload.certificate_chain);
    log::info!("SHA-256 digest computed: {}", digest);

    post_certificate(client, token, base_url, edge_id, payload).await
}

#[derive(Debug, Serialize)]
struct AuditLog {
    timestamp: String,
    event_type: String,
    caller_id: String,
    attestation_level: String,
    success: bool,
    latency_ms: u64,
    error_message: Option<String>,
}

#[derive(Debug, Serialize)]
struct CnamSyncPayload {
    #[serde(rename = "callId")]
    call_id: String,
    #[serde(rename = "attestationLevel")]
    attestation_level: String,
    #[serde(rename = "verifiedCallerId")]
    verified_caller_id: String,
    #[serde(rename = "timestamp")]
    timestamp: String,
}

struct MetricsTracker {
    total_attempts: u64,
    successful_attestations: u64,
    total_latency_ms: u64,
}

impl MetricsTracker {
    fn record_attempt(&mut self, latency: u64, success: bool) {
        self.total_attempts += 1;
        self.total_latency_ms += latency;
        if success {
            self.successful_attestations += 1;
        }
    }

    fn get_success_rate(&self) -> f64 {
        if self.total_attempts == 0 { 0.0 } else {
            (self.successful_attestations as f64 / self.total_attempts as f64) * 100.0
        }
    }
}

async fn sync_with_cnam_webhook(client: &Client, webhook_url: &str, payload: &CnamSyncPayload) -> Result<(), Box<dyn std::error::Error>> {
    let _response = client
        .post(webhook_url)
        .header("Content-Type", "application/json")
        .json(payload)
        .send()
        .await?;
    log::info!("CNAM database synchronized via webhook.");
    Ok(())
}

async fn run_attestation_pipeline(
    client: &Client,
    token: &str,
    base_url: &str,
    edge_id: &str,
    caller_id: &str,
    payload: &AttestationPayload,
    revocation_list: &RevocationList,
    cnam_webhook_url: &str,
    metrics: &mut MetricsTracker,
    audit_logs: &mut Vec<AuditLog>,
) -> Result<(), Box<dyn std::error::Error>> {
    let start = Instant::now();
    
    let result = verify_caller_id_and_attest(
        client, token, base_url, edge_id, caller_id, payload, revocation_list
    ).await;

    let latency = start.elapsed().as_millis() as u64;
    let success = result.is_ok();
    
    metrics.record_attempt(latency, success);

    let log_entry = AuditLog {
        timestamp: Utc::now().to_rfc3339(),
        event_type: "stirshaken_attestation".to_string(),
        caller_id: caller_id.to_string(),
        attestation_level: payload.attestation_level.clone(),
        success,
        latency_ms: latency,
        error_message: if !success { Some(format!("{:?}", result.unwrap_err())) } else { None },
    };
    audit_logs.push(log_entry);
    log::info!("Audit log generated: {:?}", log_entry);

    if success {
        let cnam_payload = CnamSyncPayload {
            call_id: payload.call_id.clone(),
            attestation_level: payload.attestation_level.clone(),
            verified_caller_id: caller_id.to_string(),
            timestamp: Utc::now().to_rfc3339(),
        };
        sync_with_cnam_webhook(client, cnam_webhook_url, &cnam_payload).await?;
    }

    result.map(|_| ())
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    env_logger::init();
    
    let client = Client::new();
    let mut token_cache = TokenCache::new(
        "YOUR_CLIENT_ID".to_string(),
        "YOUR_CLIENT_SECRET".to_string(),
        "https://api.mypurecloud.com".to_string(),
    );
    
    let token = token_cache.get_valid_token().await?;
    let edge_id = "your-edge-id";
    let cnam_webhook_url = "https://your-cnam-sync-endpoint.com/webhook";
    
    let payload = AttestationPayload {
        call_id: "cert-98765".to_string(),
        certificate_chain: vec![
            "-----BEGIN CERTIFICATE-----\nMIIC...".to_string(),
            "-----BEGIN CERTIFICATE-----\nMIID...".to_string(),
        ],
        trust_directive: "trust-anchor-01".to_string(),
        attestation_level: "A".to_string(),
    };

    validate_attest_schema(&payload)?;

    let revocation_list = RevocationList {
        revoked_ids: vec!["revoked-cert-001".to_string()],
    };

    let mut metrics = MetricsTracker {
        total_attempts: 0,
        successful_attestations: 0,
        total_latency_ms: 0,
    };
    let mut audit_logs = Vec::new();

    run_attestation_pipeline(
        &client, &token, "https://api.mypurecloud.com", edge_id, "+12025551234",
        &payload, &revocation_list, cnam_webhook_url, &mut metrics, &mut audit_logs
    ).await?;

    println!("Verification success rate: {:.2}%", metrics.get_success_rate());
    println!("Total attestations processed: {}", metrics.total_attempts);
    for log in &audit_logs {
        println!("Audit: {:?}", log);
    }

    Ok(())
}

Common Errors & Debugging

Error: HTTP 401 Unauthorized

  • Cause: The OAuth token has expired or the client credentials are incorrect.
  • Fix: Ensure the TokenCache refreshes the token before expiry. Verify that client_id and client_secret match the Genesys Cloud application settings.
  • Code fix: The get_valid_token method subtracts 60 seconds from expires_in to trigger early refresh. If 401 persists, regenerate credentials in the Genesys Cloud admin console.

Error: HTTP 403 Forbidden

  • Cause: The OAuth client lacks the required scopes.
  • Fix: Add telephony:edge:stirshaken:read and telephony:edge:stirshaken:write to the application scopes in Genesys Cloud.
  • Code fix: Re-authorize the client after scope updates. The token must be regenerated to include the new permissions.

Error: HTTP 400 Bad Request (Schema Validation)

  • Cause: Certificate chain exceeds the three-certificate limit, or attestation level is invalid.
  • Fix: Trim the certificate chain to the leaf, intermediate, and root certificates only. Verify attestation_level matches A, B, C, or v.
  • Code fix: The validate_attest_schema function enforces these constraints before the API call. Adjust the payload construction logic to filter expired or duplicate certificates.

Error: HTTP 429 Too Many Requests

  • Cause: Rate limit cascade across the telephony microservices.
  • Fix: Implement exponential backoff. Genesys Cloud returns Retry-After headers when possible.
  • Code fix: The post_certificate function detects 429 status codes and sleeps for five seconds before retrying. For production systems, parse the Retry-After header and scale the backoff interval.

Error: HTTP 5xx Server Error

  • Cause: Temporary telephony engine degradation or certificate parsing failure.
  • Fix: Retry with jitter. Verify PEM encoding matches RFC 7468.
  • Code fix: Wrap the pipeline in a retry loop with randomized delays between 2 and 8 seconds. Log the raw response body for Genesys Cloud support ticket creation.

Official References