Implementing Authorization Code with PKCE for Genesys Cloud SPAs

What You Will Build

• A single-page application (SPA) that authenticates users against Genesys Cloud using the Authorization Code flow with Proof Key for Code Exchange (PKCE).
• This implementation uses the Genesys Cloud v2 REST API endpoints directly via JavaScript fetch to demonstrate the underlying protocol mechanics.
• The tutorial covers the complete lifecycle: code challenge generation, authorization request, token exchange, and user profile retrieval.

Prerequisites

• Genesys Cloud Org: An active Genesys Cloud organization with API access enabled.
• OAuth Client: A public OAuth client registered in the Genesys Cloud Admin Portal.
  • Client Type: Public (Confidential clients cannot be used in pure browser-based SPAs without a backend proxy).
  • Redirect URI: Must match your development URL exactly (e.g., http://localhost:3000/callback).
• Required Scopes: view:myprofile, offline_access (optional, for refresh tokens).
• Runtime: Any modern browser supporting ES6+ and the fetch API.
• Dependencies: None. This tutorial uses native browser APIs to ensure clarity of the HTTP flow.

Authentication Setup

The core security improvement in PKCE is the prevention of authorization code interception attacks. In a traditional Authorization Code flow, an attacker could intercept the authorization code returned to your redirect URI and exchange it for an access token. PKCE mitigates this by requiring the client to generate a secret code verifier at the start of the flow. The server generates a code challenge from this verifier. When the client exchanges the authorization code for a token, it must present the original verifier. If the verifier does not match the challenge, the token exchange fails.

For SPAs, the Public client type is mandatory because there is no secure way to store a client secret in client-side code. Genesys Cloud enforces PKCE for all public clients.

Step 1: Generating the Code Verifier and Challenge

The first step occurs entirely in the client. You must generate a cryptographically random string (the code verifier) and derive a code challenge from it using SHA-256.

The Genesys Cloud API expects the code challenge to be base64url encoded. Standard base64 encoding uses + and /, which are URL-unsafe. Base64url uses - and _ instead and strips padding =.

// utils/crypto.js

/**
 * Generates a random code verifier string.
 * The verifier must be between 43 and 128 characters long.
 */
export async function generateCodeVerifier() {
  const array = new Uint8Array(32);
  window.crypto.getRandomValues(array);
  return Array.from(array, byte => byte.toString(16).padStart(2, '0')).join('');
}

/**
 * Generates the code challenge from the code verifier.
 * Uses SHA-256 hashing and base64url encoding.
 */
export async function generateCodeChallenge(codeVerifier) {
  const encoder = new TextEncoder();
  const data = encoder.encode(codeVerifier);
  const hashBuffer = await window.crypto.subtle.digest('SHA-256', data);
  
  // Convert ArrayBuffer to Base64
  const hashArray = Array.from(new Uint8Array(hashBuffer));
  const hashBase64 = btoa(hashArray.map(byte => String.fromCharCode(byte)).join(''));
  
  // Convert Base64 to Base64url
  return hashBase64.replace(/\+/g, '-').replace(/\//g, '_').replace(/=/g, '');
}

Step 2: Initiating the Authorization Request

With the code challenge in hand, you redirect the user to the Genesys Cloud authorization endpoint. You must store the code verifier in the session (e.g., sessionStorage) because it is needed for the token exchange in the next step. Do not store it in localStorage as it is vulnerable to XSS, and sessionStorage is cleared when the tab closes, reducing the window of exposure.

// auth.js

const CLIENT_ID = 'your_public_client_id';
const REDIRECT_URI = 'http://localhost:3000/callback';
const SCOPES = 'view:myprofile offline_access';
const AUTHORIZATION_ENDPOINT = 'https://api.mypurecloud.com/oauth/authorize';

export async function initiateAuthorization() {
  const codeVerifier = await generateCodeVerifier();
  const codeChallenge = await generateCodeChallenge(codeVerifier);

  // Store verifier for the token exchange step
  sessionStorage.setItem('pkce_code_verifier', codeVerifier);

  const params = new URLSearchParams({
    response_type: 'code',
    client_id: CLIENT_ID,
    redirect_uri: REDIRECT_URI,
    scope: SCOPES,
    code_challenge: codeChallenge,
    code_challenge_method: 'S256', // Explicitly specify S256 for PKCE
    state: generateRandomState() // Always use a state parameter to prevent CSRF
  });

  const authUrl = `${AUTHORIZATION_ENDPOINT}?${params.toString()}`;
  window.location.href = authUrl;
}

function generateRandomState() {
  return Math.random().toString(36).substring(2);
}

Request Parameters Explained:

• response_type=code: Indicates the Authorization Code flow.
• code_challenge: The SHA-256 hashed verifier.
• code_challenge_method=S256: Tells Genesys Cloud to use SHA-256. Do not use plain in production.
• scope: Space-separated list of required permissions. view:myprofile allows reading the user’s basic profile.

Step 3: Handling the Redirect and Token Exchange

After the user authenticates and consents, Genesys Cloud redirects back to your redirect_uri with a code and state parameter. You must:

1. Verify the state parameter matches the one you generated (CSRF protection).
2. Exchange the authorization code for an access token using the /oauth/token endpoint.
3. Include the original code_verifier in this request.

// auth.js

const TOKEN_ENDPOINT = 'https://api.mypurecloud.com/oauth/token';

export async function handleCallback() {
  const urlParams = new URLSearchParams(window.location.search);
  const code = urlParams.get('code');
  const state = urlParams.get('state');
  const error = urlParams.get('error');

  // Handle authorization errors (e.g., user denied consent)
  if (error) {
    console.error('Authorization failed:', error);
    return null;
  }

  if (!code) {
    console.error('No authorization code found in URL');
    return null;
  }

  // Retrieve the verifier stored in Step 2
  const codeVerifier = sessionStorage.getItem('pkce_code_verifier');
  if (!codeVerifier) {
    console.error('Code verifier not found in session');
    return null;
  }

  try {
    const tokenResponse = await exchangeCodeForToken(code, codeVerifier);
    return tokenResponse;
  } catch (err) {
    console.error('Token exchange failed:', err);
    return null;
  }
}

async function exchangeCodeForToken(code, codeVerifier) {
  const requestBody = new URLSearchParams({
    grant_type: 'authorization_code',
    code: code,
    client_id: CLIENT_ID,
    redirect_uri: REDIRECT_URI,
    code_verifier: codeVerifier
  });

  const response = await fetch(TOKEN_ENDPOINT, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/x-www-form-urlencoded',
      'Accept': 'application/json'
    },
    body: requestBody
  });

  if (!response.ok) {
    const errorData = await response.json();
    throw new Error(`Token exchange failed: ${errorData.error_description || response.statusText}`);
  }

  return await response.json();
}

Expected Response Body:

{
  "access_token": "eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9...",
  "token_type": "Bearer",
  "expires_in": 1800,
  "refresh_token": "dGhpcyBpcyBhIHJlZnJlc2ggdG9rZW4...",
  "scope": "view:myprofile offline_access",
  "id_token": "eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9..."
}

Note that offline_access in the scope results in a refresh_token. Without it, you only receive an access_token and id_token.

Step 4: Using the Access Token

Once you have the access token, you can call Genesys Cloud APIs. The token must be passed in the Authorization header as a Bearer token.

// api.js

const API_BASE = 'https://api.mypurecloud.com/api/v2';

export async function getUserProfile(accessToken) {
  const response = await fetch(`${API_BASE}/users/me`, {
    method: 'GET',
    headers: {
      'Authorization': `Bearer ${accessToken}`,
      'Accept': 'application/json'
    }
  });

  if (!response.ok) {
    if (response.status === 401) {
      throw new Error('Access token expired or invalid');
    }
    throw new Error(`API request failed: ${response.statusText}`);
  }

  return await response.json();
}

Required Scope: view:myprofile

Complete Working Example

Below is a single-file HTML/JS application that demonstrates the entire flow. Save this as index.html and serve it via a local server (e.g., npx serve . or python -m http.server).

Replace YOUR_CLIENT_ID and YOUR_REDIRECT_URI with your actual values.

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Genesys Cloud PKCE Auth Demo</title>
    <style>
        body { font-family: sans-serif; padding: 2rem; max-width: 800px; margin: 0 auto; }
        .hidden { display: none; }
        button { padding: 10px 20px; cursor: pointer; background: #0052cc; color: white; border: none; border-radius: 4px; }
        button:hover { background: #0043a8; }
        pre { background: #f4f4f4; padding: 1rem; border-radius: 4px; overflow-x: auto; }
        .error { color: #d32f2f; }
        .success { color: #2e7d32; }
    </style>
</head>
<body>
    <h1>Genesys Cloud PKCE Authentication</h1>

    <div id="login-section">
        <p>Click the button to authenticate with Genesys Cloud using PKCE.</p>
        <button id="login-btn">Login with Genesys Cloud</button>
    </div>

    <div id="loading-section" class="hidden">
        <p>Processing authentication...</p>
    </div>

    <div id="result-section" class="hidden">
        <h2>Authentication Result</h2>
        <pre id="result-output"></pre>
        <button id="logout-btn" style="background: #d32f2f;">Logout</button>
    </div>

    <script>
        // --- Configuration ---
        const CLIENT_ID = 'YOUR_CLIENT_ID'; 
        const REDIRECT_URI = window.location.origin + window.location.pathname;
        const AUTH_ENDPOINT = 'https://api.mypurecloud.com/oauth/authorize';
        const TOKEN_ENDPOINT = 'https://api.mypurecloud.com/oauth/token';
        const API_BASE = 'https://api.mypurecloud.com/api/v2';
        const SCOPES = 'view:myprofile offline_access';

        // --- Crypto Utilities ---
        async function generateCodeVerifier() {
            const array = new Uint8Array(32);
            window.crypto.getRandomValues(array);
            return Array.from(array, byte => byte.toString(16).padStart(2, '0')).join('');
        }

        async function generateCodeChallenge(verifier) {
            const encoder = new TextEncoder();
            const data = encoder.encode(verifier);
            const hashBuffer = await window.crypto.subtle.digest('SHA-256', data);
            const hashArray = Array.from(new Uint8Array(hashBuffer));
            const hashBase64 = btoa(hashArray.map(byte => String.fromCharCode(byte)).join(''));
            return hashBase64.replace(/\+/g, '-').replace(/\//g, '_').replace(/=/g, '');
        }

        function generateState() {
            return Math.random().toString(36).substring(2);
        }

        // --- Auth Flow ---
        async function initiateLogin() {
            const codeVerifier = await generateCodeVerifier();
            const codeChallenge = await generateCodeChallenge(codeVerifier);
            const state = generateState();

            sessionStorage.setItem('pkce_verifier', codeVerifier);
            sessionStorage.setItem('pkce_state', state);

            const params = new URLSearchParams({
                response_type: 'code',
                client_id: CLIENT_ID,
                redirect_uri: REDIRECT_URI,
                scope: SCOPES,
                code_challenge: codeChallenge,
                code_challenge_method: 'S256',
                state: state
            });

            window.location.href = `${AUTH_ENDPOINT}?${params.toString()}`;
        }

        async function handleCallback() {
            const urlParams = new URLSearchParams(window.location.search);
            const code = urlParams.get('code');
            const state = urlParams.get('state');
            const error = urlParams.get('error');

            if (error) {
                showError(`Authorization Error: ${error}`);
                return;
            }

            if (!code) {
                return; // No code, do nothing
            }

            const storedState = sessionStorage.getItem('pkce_state');
            const codeVerifier = sessionStorage.getItem('pkce_verifier');

            if (!storedState || state !== storedState) {
                showError('State mismatch. Potential CSRF attack.');
                return;
            }

            try {
                const tokens = await exchangeCode(code, codeVerifier);
                const userProfile = await getUserProfile(tokens.access_token);
                showResult({ ...tokens, user: userProfile });
            } catch (err) {
                showError(err.message);
            }
        }

        async function exchangeCode(code, codeVerifier) {
            const body = new URLSearchParams({
                grant_type: 'authorization_code',
                code: code,
                client_id: CLIENT_ID,
                redirect_uri: REDIRECT_URI,
                code_verifier: codeVerifier
            });

            const res = await fetch(TOKEN_ENDPOINT, {
                method: 'POST',
                headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
                body: body
            });

            if (!res.ok) {
                const errData = await res.json();
                throw new Error(errData.error_description || 'Token exchange failed');
            }
            return await res.json();
        }

        async function getUserProfile(accessToken) {
            const res = await fetch(`${API_BASE}/users/me`, {
                headers: { 'Authorization': `Bearer ${accessToken}` }
            });
            if (!res.ok) throw new Error('Failed to fetch user profile');
            return await res.json();
        }

        // --- UI Helpers ---
        function showResult(data) {
            document.getElementById('login-section').classList.add('hidden');
            document.getElementById('loading-section').classList.add('hidden');
            document.getElementById('result-section').classList.remove('hidden');
            document.getElementById('result-output').textContent = JSON.stringify(data, null, 2);
        }

        function showError(msg) {
            document.getElementById('login-section').classList.add('hidden');
            document.getElementById('loading-section').classList.add('hidden');
            document.getElementById('result-section').classList.remove('hidden');
            const output = document.getElementById('result-output');
            output.className = 'error';
            output.textContent = msg;
        }

        function logout() {
            sessionStorage.clear();
            location.reload();
        }

        // --- Initialization ---
        document.getElementById('login-btn').addEventListener('click', initiateLogin);
        document.getElementById('logout-btn').addEventListener('click', logout);

        // Check if we are returning from auth
        if (window.location.search.includes('code')) {
            document.getElementById('login-section').classList.add('hidden');
            document.getElementById('loading-section').classList.remove('hidden');
            handleCallback();
        }
    </script>
</body>
</html>

Common Errors & Debugging

Error: invalid_grant

What causes it:
This is the most common error during the token exchange step. It typically means the authorization code has expired (they are valid for only 5 minutes), was already used, or the code_verifier does not match the code_challenge sent in the initial authorization request.

How to fix it:

1. Ensure you are using the exact same code_verifier that was used to generate the code_challenge.
2. Check for typos in the base64url encoding. Ensure + is replaced with -, / with _, and = is removed.
3. Verify that the redirect_uri in the token request matches the redirect_uri in the authorization request exactly.

Code showing the fix:

// Ensure this matches the string stored in sessionStorage
const codeVerifier = sessionStorage.getItem('pkce_code_verifier');
if (!codeVerifier) {
    throw new Error("Code verifier missing. Did the page refresh unexpectedly?");
}

Error: invalid_client

What causes it:
The client_id provided is invalid, not registered as a public client, or does not have the correct redirect URI whitelisted.

How to fix it:

1. Verify the client_id in your code matches the ID in the Genesys Cloud Admin Portal > Security > OAuth.
2. Ensure the Client Type is set to Public.
3. Ensure the redirect_uri in your code is exactly listed in the OAuth client’s “Allowed Redirect URIs” list. Trailing slashes matter.

Error: 401 Unauthorized on API Calls

What causes it:
The access token is expired, malformed, or lacks the required scope.

How to fix it:

1. Check the expires_in value from the token response. Access tokens default to 30 minutes.
2. If you included offline_access, use the refresh_token to get a new access token without re-authenticating the user.

Refreshing the Token:

async function refreshToken(refreshToken) {
    const body = new URLSearchParams({
        grant_type: 'refresh_token',
        client_id: CLIENT_ID,
        refresh_token: refreshToken
    });

    const res = await fetch(TOKEN_ENDPOINT, {
        method: 'POST',
        headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
        body: body
    });

    if (!res.ok) {
        throw new Error('Token refresh failed');
    }
    return await res.json();
}

Error: 400 Bad Request with invalid_request

What causes it:
Missing required parameters in the authorization or token request.

How to fix it:

1. Ensure response_type=code is present in the auth URL.
2. Ensure grant_type=authorization_code is present in the token request.
3. Ensure code_challenge and code_challenge_method are present in the auth URL for public clients.

Official References

• Genesys Cloud OAuth 2.0 Documentation
• RFC 7636: Proof Key for Code Exchange by OAuth Public Clients
• Genesys Cloud API Explorer