Implementing OAuth2 PKCE for Genesys Cloud Plugin Authentication with TypeScript

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Implementing OAuth2 PKCE for Genesys Cloud Plugin Authentication with TypeScript

What You Will Build

A production-ready TypeScript module that generates PKCE parameters, redirects users to Genesys Cloud authorization, exchanges the returned authorization code for an access token with retry logic, and initializes the @genesyscloud/purecloud-platform-client-v2 SDK to query authenticated data. This tutorial covers the complete authorization code flow with Proof Key for Code Exchange. The implementation uses TypeScript, modern browser APIs, and the official Genesys Cloud Platform SDK.

Prerequisites

  • Genesys Cloud OAuth client registered with public or confidential type and PKCE enabled
  • Required OAuth scopes: plugin:read, user:me:read, user:read
  • SDK: @genesyscloud/purecloud-platform-client-v2 version 5.0 or higher
  • Runtime: Node.js 18+ or modern browser supporting crypto.subtle
  • External dependencies: axios for HTTP requests with automatic 429 retry handling, @types/node if running in Node

Authentication Setup

Genesys Cloud uses standard OAuth 2.1 endpoints for authorization and token exchange. The PKCE extension secures public clients by binding the authorization request to the token exchange request. You must generate a cryptographically random code_verifier, derive a code_challenge using SHA-256 and base64url encoding, and pass both values through the authorization and token endpoints.

The authorization endpoint resides at https://{env}.mypurecloud.com/oauth/authorize. The token endpoint resides at https://{env}.mypurecloud.com/oauth/token. The SDK does not handle PKCE parameter generation natively, so you will manage the cryptographic steps and token exchange manually before injecting the resulting access token into the PlatformClient instance.

Implementation

Step 1: Generate PKCE Parameters

PKCE requires a random code verifier between 43 and 128 characters. You derive the challenge by hashing the verifier with SHA-256 and applying base64url encoding. This prevents authorization code interception attacks on public clients.

/**
 * Generates a cryptographically secure random string for the code_verifier.
 * Returns a 64-character hexadecimal string.
 */
export function generateCodeVerifier(): string {
  const array = new Uint8Array(32);
  crypto.getRandomValues(array);
  return Array.from(array, (byte) => byte.toString(16).padStart(2, '0')).join('');
}

/**
 * Derives the code_challenge from the code_verifier using SHA-256 and base64url encoding.
 * Required for code_challenge_method=S256.
 */
export async function generateCodeChallenge(verifier: string): Promise<string> {
  const encoder = new TextEncoder();
  const data = encoder.encode(verifier);
  const hashBuffer = await crypto.subtle.digest('SHA-256', data);
  const hashArray = new Uint8Array(hashBuffer);
  
  // Convert to base64url: replace + with -, / with _, strip padding =
  return btoa(String.fromCharCode(...hashArray))
    .replace(/\+/g, '-')
    .replace(/\//g, '_')
    .replace(/=+$/, '');
}

Step 2: Construct Authorization URL and Handle Callback

You construct the authorization URL with the required parameters. Genesys Cloud requires response_type=code, client_id, redirect_uri, scope, code_challenge, code_challenge_method, and a state parameter for CSRF protection. You redirect the browser to this URL. After the user grants consent, Genesys Cloud redirects back to your redirect_uri with a code and state query parameter.

interface AuthConfig {
  env: string;
  clientId: string;
  redirectUri: string;
  scopes: string[];
}

export function buildAuthorizationUrl(config: AuthConfig, challenge: string, state: string): string {
  const baseUrl = `https://${config.env}.mypurecloud.com/oauth/authorize`;
  const params = new URLSearchParams({
    response_type: 'code',
    client_id: config.clientId,
    redirect_uri: config.redirectUri,
    scope: config.scopes.join(' '),
    code_challenge: challenge,
    code_challenge_method: 'S256',
    state: state
  });
  return `${baseUrl}?${params.toString()}`;
}

export function extractAuthCallback(url: string): { code: string; state: string } | null {
  const searchParams = new URL(url).searchParams;
  const code = searchParams.get('code');
  const state = searchParams.get('state');
  const error = searchParams.get('error');
  
  if (error) throw new Error(`Authorization failed: ${error} - ${searchParams.get('error_description')}`);
  if (!code || !state) return null;
  
  return { code, state };
}

Step 3: Exchange Authorization Code for Access Token

You send the authorization code to the token endpoint. The request body must include grant_type=authorization_code, the code, redirect_uri, client_id, and the original code_verifier. You must implement retry logic for HTTP 429 responses to handle Genesys Cloud rate limiting. The response returns an access_token, refresh_token, expires_in, and scope.

HTTP Request Cycle:

  • Method: POST
  • Path: /oauth/token
  • Headers: Content-Type: application/x-www-form-urlencoded
  • Body: grant_type=authorization_code&code={code}&redirect_uri={uri}&client_id={id}&code_verifier={verifier}

Expected Response:

{
  "access_token": "eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9...",
  "refresh_token": "dGhpcyBpcyBhIHJlZnJlc2ggdG9rZW4...",
  "token_type": "Bearer",
  "expires_in": 900,
  "scope": "plugin:read user:me:read user:read"
}

import axios, { AxiosError } from 'axios';

interface TokenResponse {
  access_token: string;
  refresh_token: string;
  token_type: string;
  expires_in: number;
  scope: string;
}

export async function exchangeCodeForToken(
  config: AuthConfig,
  code: string,
  verifier: string
): Promise<TokenResponse> {
  const tokenUrl = `https://${config.env}.mypurecloud.com/oauth/token`;
  
  const payload = new URLSearchParams({
    grant_type: 'authorization_code',
    code: code,
    redirect_uri: config.redirectUri,
    client_id: config.clientId,
    code_verifier: verifier
  });

  const client = axios.create({
    baseURL: tokenUrl,
    timeout: 10000,
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' }
  });

  // Retry configuration for 429 Too Many Requests
  client.interceptors.response.use(
    (response) => response,
    async (error: AxiosError) => {
      if (error.response?.status === 429) {
        const retryAfter = error.response.headers['retry-after'] 
          ? parseInt(error.response.headers['retry-after'], 10) * 1000 
          : 1000;
        await new Promise((resolve) => setTimeout(resolve, retryAfter));
        return client.post(payload.toString());
      }
      throw error;
    }
  );

  try {
    const response = await client.post('', payload.toString());
    return response.data;
  } catch (error) {
    if (error instanceof AxiosError) {
      const status = error.response?.status;
      if (status === 400) throw new Error('Invalid grant: code_verifier mismatch or expired code');
      if (status === 401) throw new Error('Invalid client_id or unauthorized redirect_uri');
      if (status === 403) throw new Error('Insufficient scope or client misconfigured');
    }
    throw error;
  }
}

Step 4: Initialize PlatformClient and Query User Data

After obtaining the access token, you inject it into the Genesys Cloud TypeScript SDK. The PlatformClient handles authentication headers automatically. You will query /api/v2/users to demonstrate pagination and verify scope permissions. The endpoint requires user:read scope.

import { PlatformClient } from '@genesyscloud/purecloud-platform-client-v2';

export async function queryUsersWithPagination(
  env: string,
  accessToken: string,
  pageSize: number = 25
): Promise<any[]> {
  const platformClient = new PlatformClient();
  platformClient.setEnvironment(env);
  platformClient.setAccessToken(accessToken);

  const allUsers: any[] = [];
  let nextPage = '';
  let hasNext = true;

  while (hasNext) {
    const response = await platformClient.usersApi.getUserPage({
      pageSize: pageSize,
      nextPage: nextPage || undefined
    });

    if (response.body?.entities) {
      allUsers.push(...response.body.entities);
    }

    if (response.body?.nextPage) {
      nextPage = response.body.nextPage;
    } else {
      hasNext = false;
    }
  }

  return allUsers;
}

Complete Working Example

The following module integrates all steps into a single authentication flow. You can run this in a browser environment or Node.js with the crypto polyfill. Replace placeholder values with your actual Genesys Cloud environment and OAuth client credentials.

import axios from 'axios';
import { PlatformClient } from '@genesyscloud/purecloud-platform-client-v2';

// Configuration
const CONFIG = {
  env: 'usw2.pure.cloud', // Replace with your environment
  clientId: 'YOUR_CLIENT_ID',
  redirectUri: 'http://localhost:3000/callback',
  scopes: ['plugin:read', 'user:me:read', 'user:read']
};

// PKCE Utilities
function generateCodeVerifier(): string {
  const array = new Uint8Array(32);
  crypto.getRandomValues(array);
  return Array.from(array, (b) => b.toString(16).padStart(2, '0')).join('');
}

async function generateCodeChallenge(verifier: string): Promise<string> {
  const encoder = new TextEncoder();
  const data = encoder.encode(verifier);
  const hashBuffer = await crypto.subtle.digest('SHA-256', data);
  const hashArray = new Uint8Array(hashBuffer);
  return btoa(String.fromCharCode(...hashArray))
    .replace(/\+/g, '-')
    .replace(/\//g, '_')
    .replace(/=+$/, '');
}

// Authorization Flow
async function initiateAuth(): Promise<void> {
  const verifier = generateCodeVerifier();
  const challenge = await generateCodeChallenge(verifier);
  const state = Math.random().toString(36).substring(2, 15);
  
  // Store verifier and state for callback validation
  sessionStorage.setItem('pkce_verifier', verifier);
  sessionStorage.setItem('pkce_state', state);

  const params = new URLSearchParams({
    response_type: 'code',
    client_id: CONFIG.clientId,
    redirect_uri: CONFIG.redirectUri,
    scope: CONFIG.scopes.join(' '),
    code_challenge: challenge,
    code_challenge_method: 'S256',
    state: state
  });

  window.location.href = `https://${CONFIG.env}.mypurecloud.com/oauth/authorize?${params.toString()}`;
}

// Token Exchange
async function handleCallback(url: string): Promise<string> {
  const searchParams = new URL(url).searchParams;
  const code = searchParams.get('code');
  const state = searchParams.get('state');
  const storedState = sessionStorage.getItem('pkce_state');
  const verifier = sessionStorage.getItem('pkce_verifier');

  if (!code || !state || !storedState || !verifier) {
    throw new Error('Missing authorization parameters or session data');
  }

  if (state !== storedState) {
    throw new Error('State mismatch: potential CSRF attack detected');
  }

  const tokenUrl = `https://${CONFIG.env}.mypurecloud.com/oauth/token`;
  const payload = new URLSearchParams({
    grant_type: 'authorization_code',
    code: code,
    redirect_uri: CONFIG.redirectUri,
    client_id: CONFIG.clientId,
    code_verifier: verifier
  });

  const client = axios.create({
    baseURL: tokenUrl,
    timeout: 10000,
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' }
  });

  client.interceptors.response.use(
    (response) => response,
    async (error: any) => {
      if (error.response?.status === 429) {
        const retryAfter = error.response.headers['retry-after'] 
          ? parseInt(error.response.headers['retry-after'], 10) * 1000 
          : 1000;
        await new Promise((resolve) => setTimeout(resolve, retryAfter));
        return client.post(payload.toString());
      }
      throw error;
    }
  );

  const response = await client.post('', payload.toString());
  sessionStorage.removeItem('pkce_verifier');
  sessionStorage.removeItem('pkce_state');
  return response.data.access_token;
}

// SDK Usage
async function verifyAuthentication(accessToken: string): Promise<void> {
  const platformClient = new PlatformClient();
  platformClient.setEnvironment(CONFIG.env);
  platformClient.setAccessToken(accessToken);

  try {
    const me = await platformClient.usersApi.getUserMe();
    console.log('Authenticated user:', me.body);
  } catch (error) {
    console.error('API call failed:', error);
  }
}

// Execution entry point
async function main(): Promise<void> {
  const url = window.location.href;
  if (url.includes('code=') && url.includes('state=')) {
    const token = await handleCallback(url);
    await verifyAuthentication(token);
  } else {
    await initiateAuth();
  }
}

main();

Common Errors & Debugging

Error: 400 Bad Request (Invalid Grant)

Genesys Cloud returns this when the code_verifier does not match the hashed code_challenge sent during authorization, or when the authorization code has expired. Authorization codes expire after 10 minutes. Ensure you store the verifier in the same session context and reuse it exactly during the token exchange. Verify your base64url encoding strips padding characters correctly.

Error: 401 Unauthorized

This indicates an invalid client_id or a redirect_uri that does not match the registered OAuth client configuration exactly. Genesys Cloud performs strict URL matching including trailing slashes. Check your OAuth client settings in the Genesys Cloud admin console under Platform > OAuth.

Error: 403 Forbidden

The access token lacks the required scope for the requested API endpoint. The /api/v2/users endpoint requires user:read. The /api/v2/users/me endpoint requires user:me:read. If you receive 403, verify the scope parameter in your authorization URL matches the registered client permissions and the API documentation requirements.

Error: 429 Too Many Requests

Genesys Cloud enforces rate limits per client and per endpoint. The token exchange endpoint has a lower threshold than standard API calls. The provided axios interceptor handles automatic retry by reading the Retry-After header. If you encounter persistent 429 errors, implement exponential backoff and reduce concurrent authorization attempts.

Error: CORS Policy Blocked

Browser-based token exchanges require your redirect_uri domain to be whitelisted in the OAuth client configuration. Genesys Cloud does not allow wildcard origins. You must register each exact domain and path. If you are developing locally, register http://localhost:3000/callback explicitly.

Official References