Token Management - Baanx API Documentation

Overview

Understanding token lifecycle management is critical for building reliable applications. This guide covers everything you need to know about handling JWT tokens, access tokens, and refresh tokens throughout your application’s lifecycle.

Token Types

The API uses three distinct token types, each serving a specific purpose:

JWT Token

OAuth Flow Session

Lifetime: 10 minutes
Purpose: OAuth flow coordination
Usage: Only during OAuth authorization
Not for API calls

Access Token

API Authentication

Lifetime: 6 hours
Purpose: Authenticate API requests
Usage: All authenticated endpoints
Include in Authorization header

Refresh Token

Token Renewal

Lifetime: 7 days
Purpose: Obtain new access tokens
Usage: Token refresh endpoint
Store securely, never expose

Token Lifecycle

JWT Token (OAuth Session)

Purpose

The JWT token is used only during the OAuth authorization flow to maintain session state between OAuth steps.

Not for API Calls: This token is NOT used for authenticating API requests. It’s exclusively for OAuth flow coordination.

Characteristics

Property	Value
Lifetime	10 minutes
Obtained from	`GET /v1/auth/oauth/authorize/initiate`
Used in	`POST /v1/auth/oauth/authorize` (API mode only)
Format	JWT (JSON Web Token)
Renewal	Not renewable - restart OAuth flow

Usage Example

// Step 1: Get JWT token
const { token: jwtToken } = await initiateOAuth();

// Step 3: Use JWT token (API mode only)
await fetch('/v1/auth/oauth/authorize', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${accessTokenFromLogin}`,
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    token: jwtToken  // JWT token goes in body, not header
  })
});

Expiration Handling

const SESSION_TIMEOUT = 10 * 60 * 1000; // 10 minutes

class OAuthSession {
  private startTime: number;
  private jwtToken: string;

  constructor(token: string) {
    this.jwtToken = token;
    this.startTime = Date.now();
  }

  isExpired(): boolean {
    return Date.now() - this.startTime >= SESSION_TIMEOUT;
  }

  getToken(): string {
    if (this.isExpired()) {
      throw new Error('OAuth session expired. Please restart authorization flow.');
    }
    return this.jwtToken;
  }

  getRemainingTime(): number {
    return Math.max(0, SESSION_TIMEOUT - (Date.now() - this.startTime));
  }
}

Access Token (API Authentication)

Purpose

Access tokens authorize your application to make API requests on behalf of the user. Include them in the Authorization: Bearer header to perform user-authorized operations.

Acting on Behalf of Users: Access tokens represent the user’s grant of permission for your application to interact with their account. Use them only for actions the user has authorized.

Characteristics

Property	Value
Lifetime	6 hours (21,600 seconds)
Obtained from	`POST /v1/auth/oauth/token` or `POST /v1/auth/login`
Used in	Authorization header for all authenticated endpoints
Format	JWT (JSON Web Token)
Renewal	Via refresh token

Usage

async function callAPI(endpoint: string) {
  const accessToken = await getAccessToken();

  const response = await fetch(`https://api.example.com${endpoint}`, {
    headers: {
      'Authorization': `Bearer ${accessToken}`,
      'x-client-key': process.env.CLIENT_KEY!
    }
  });

  return response.json();
}

// Examples
const user = await callAPI('/v1/users/me');
const wallets = await callAPI('/v1/wallets');
const cards = await callAPI('/v1/cards');

Storage

Web Applications
Mobile Applications
Server-Side

Recommended: HTTP-only Cookies

// Server-side: Set HTTP-only cookie
res.cookie('access_token', token, {
  httpOnly: true,
  secure: true,
  sameSite: 'strict',
  maxAge: 6 * 60 * 60 * 1000 // 6 hours
});

// Client-side: Cookie sent automatically
fetch('/api/protected', {
  credentials: 'include'
});

Alternative: Memory Storage (for SPAs)

// Store in application state, not localStorage
class TokenManager {
  private accessToken: string | null = null;

  setToken(token: string) {
    this.accessToken = token;
  }

  getToken(): string | null {
    return this.accessToken;
  }

  clearToken() {
    this.accessToken = null;
  }
}

Avoid localStorage for sensitive applications: XSS attacks can steal tokens from localStorage. Use HTTP-only cookies or memory storage instead.

Use Platform Secure Storage

// React Native: Use expo-secure-store or react-native-keychain
import * as SecureStore from 'expo-secure-store';

async function storeToken(token: string) {
  await SecureStore.setItemAsync('access_token', token);
}

async function getToken(): Promise<string | null> {
  return await SecureStore.getItemAsync('access_token');
}

async function deleteToken() {
  await SecureStore.deleteItemAsync('access_token');
}

// iOS: Use Keychain
import KeychainSwift

let keychain = KeychainSwift()

func storeToken(_ token: String) {
    keychain.set(token, forKey: "access_token")
}

func getToken() -> String? {
    return keychain.get("access_token")
}

func deleteToken() {
    keychain.delete("access_token")
}

// Android: Use EncryptedSharedPreferences
import androidx.security.crypto.EncryptedSharedPreferences
import androidx.security.crypto.MasterKey

val masterKey = MasterKey.Builder(context)
    .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
    .build()

val sharedPreferences = EncryptedSharedPreferences.create(
    context,
    "secure_prefs",
    masterKey,
    EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
    EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
)

fun storeToken(token: String) {
    sharedPreferences.edit().putString("access_token", token).apply()
}

fun getToken(): String? {
    return sharedPreferences.getString("access_token", null)
}

Session or Database Storage

// Express.js with session
app.post('/oauth/callback', async (req, res) => {
  const tokens = await exchangeCodeForTokens(req.query.code);

  req.session.accessToken = tokens.access_token;
  req.session.refreshToken = tokens.refresh_token;
  req.session.tokenExpiry = Date.now() + (tokens.expires_in * 1000);

  res.redirect('/dashboard');
});

// Middleware to check token
async function requireAuth(req, res, next) {
  if (Date.now() >= req.session.tokenExpiry) {
    req.session.accessToken = await refreshToken(req.session.refreshToken);
    req.session.tokenExpiry = Date.now() + (6 * 60 * 60 * 1000);
  }
  next();
}

# Flask with database storage
@app.route('/oauth/callback')
def oauth_callback():
    code = request.args.get('code')
    tokens = exchange_code_for_tokens(code)

    # Store in database
    db.session.query(UserToken).filter_by(user_id=current_user.id).update({
        'access_token': tokens['access_token'],
        'refresh_token': tokens['refresh_token'],
        'expires_at': datetime.now() + timedelta(hours=6)
    })
    db.session.commit()

    return redirect('/dashboard')

Expiration Detection

interface TokenInfo {
  token: string;
  expiresAt: number;
}

class TokenManager {
  private tokenInfo: TokenInfo | null = null;

  setToken(token: string, expiresIn: number) {
    this.tokenInfo = {
      token,
      expiresAt: Date.now() + (expiresIn * 1000)
    };
  }

  isExpired(): boolean {
    if (!this.tokenInfo) return true;

    // Add 60 second buffer to refresh before actual expiry
    return Date.now() >= (this.tokenInfo.expiresAt - 60000);
  }

  async getValidToken(): Promise<string> {
    if (this.isExpired()) {
      await this.refreshToken();
    }
    return this.tokenInfo!.token;
  }

  private async refreshToken() {
    const refreshToken = await getRefreshToken();
    const tokens = await exchangeRefreshToken(refreshToken);
    this.setToken(tokens.access_token, tokens.expires_in);
  }
}

Best Practice: Refresh tokens 60 seconds before expiry to account for network latency and clock differences.

Refresh Token (Token Renewal)

Purpose

Refresh tokens allow you to obtain new access tokens without requiring the user to re-authenticate, providing a balance between security and user convenience.

Security for Financial Operations: Given that this API handles sensitive financial operations (setting PINs, adding funds, connecting wallets, card management), the refresh token lifetime is intentionally short at 7 days. This aligns with modern banking security standards where US financial institutions now require re-authentication after 15 minutes of inactivity.

With Biometric Authentication: If your application implements FaceID, TouchID, or credential saving, the 7-day refresh token lifetime provides a good balance between security and user experience. Users authenticate frequently with biometrics while maintaining secure access.

Characteristics

Property	Value
Lifetime	7 days (604,800 seconds)
Obtained from	`POST /v1/auth/oauth/token` (authorization_code grant)
Used in	`POST /v1/auth/oauth/token` (refresh_token grant)
Format	Opaque string
Single Use	No - can be reused until expiry

Step-Up Authentication for Privileged Operations

Critical Security Requirement: Certain privileged operations require step-up authentication regardless of token validity. Users must re-authenticate immediately before performing these actions.

Privileged operations requiring step-up authentication:

Setting or changing PIN codes
Adding or withdrawing funds
Connecting new wallets (custodial or non-custodial)
Card activation or sensitive card operations
Updating security settings
Large transactions above threshold

Implementation:

async function performPrivilegedOperation(operation: string) {
  // Check if step-up authentication is recent (within 15 minutes)
  const lastStepUp = getLastStepUpTimestamp();
  const fifteenMinutes = 15 * 60 * 1000;

  if (!lastStepUp || Date.now() - lastStepUp > fifteenMinutes) {
    // Require fresh authentication
    const authenticated = await promptBiometricOrPassword();
    if (!authenticated) {
      throw new Error('Step-up authentication required');
    }
    setLastStepUpTimestamp(Date.now());
  }

  // Proceed with privileged operation
  await executePrivilegedOperation(operation);
}

Refresh Flow

async function refreshAccessToken(): Promise<TokenResponse> {
  const refreshToken = await secureStorage.get('refresh_token');

  const response = await fetch('https://api.example.com/v1/auth/oauth/token', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'x-client-key': process.env.CLIENT_KEY!,
      'x-secret-key': process.env.SECRET_KEY!
    },
    body: JSON.stringify({
      grant_type: 'refresh_token',
      refresh_token: refreshToken
    })
  });

  if (!response.ok) {
    if (response.status === 401) {
      // Refresh token expired or invalid
      throw new Error('REFRESH_TOKEN_EXPIRED');
    }
    throw new Error('Token refresh failed');
  }

  const tokens = await response.json();

  // Update stored tokens
  await secureStorage.set('access_token', tokens.access_token);
  await secureStorage.set('refresh_token', tokens.refresh_token);
  await secureStorage.set('token_expiry', Date.now() + (tokens.expires_in * 1000));

  return tokens;
}

Response:

{
  "access_token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...",
  "token_type": "Bearer",
  "expires_in": 21600,
  "refresh_token": "def50200a1b2c3d4e5f6...",
  "refresh_token_expires_in": 604800
}

Token Rotation: The API returns a NEW refresh token with each refresh. Always update your stored refresh token.

Automatic Refresh Strategy

Implement automatic token refresh in your API client:

class APIClient {
  private isRefreshing = false;
  private refreshPromise: Promise<string> | null = null;

  async request(endpoint: string, options: RequestInit = {}) {
    let token = await this.getValidToken();

    const response = await fetch(`${this.baseURL}${endpoint}`, {
      ...options,
      headers: {
        ...options.headers,
        'Authorization': `Bearer ${token}`,
        'x-client-key': this.clientKey
      }
    });

    // If 401, token might be expired - try refreshing once
    if (response.status === 401) {
      token = await this.refreshAccessToken();

      // Retry with new token
      return fetch(`${this.baseURL}${endpoint}`, {
        ...options,
        headers: {
          ...options.headers,
          'Authorization': `Bearer ${token}`,
          'x-client-key': this.clientKey
        }
      });
    }

    return response;
  }

  private async getValidToken(): Promise<string> {
    const expiry = await secureStorage.get('token_expiry');

    // Refresh if within 60 seconds of expiry
    if (Date.now() >= (Number(expiry) - 60000)) {
      return this.refreshAccessToken();
    }

    return secureStorage.get('access_token');
  }

  private async refreshAccessToken(): Promise<string> {
    // Prevent multiple simultaneous refresh calls
    if (this.isRefreshing) {
      return this.refreshPromise!;
    }

    this.isRefreshing = true;
    this.refreshPromise = this.doRefresh();

    try {
      const token = await this.refreshPromise;
      return token;
    } finally {
      this.isRefreshing = false;
      this.refreshPromise = null;
    }
  }

  private async doRefresh(): Promise<string> {
    const refreshToken = await secureStorage.get('refresh_token');

    const response = await fetch(`${this.baseURL}/v1/auth/oauth/token`, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'x-client-key': this.clientKey,
        'x-secret-key': this.secretKey
      },
      body: JSON.stringify({
        grant_type: 'refresh_token',
        refresh_token: refreshToken
      })
    });

    if (!response.ok) {
      // Refresh token expired - need to re-authenticate
      await this.handleAuthenticationRequired();
      throw new Error('REFRESH_FAILED');
    }

    const tokens = await response.json();

    await secureStorage.set('access_token', tokens.access_token);
    await secureStorage.set('refresh_token', tokens.refresh_token);
    await secureStorage.set('token_expiry', Date.now() + (tokens.expires_in * 1000));

    return tokens.access_token;
  }

  private async handleAuthenticationRequired() {
    // Clear tokens
    await secureStorage.remove('access_token');
    await secureStorage.remove('refresh_token');
    await secureStorage.remove('token_expiry');

    // Redirect to login or show login modal
    window.location.href = '/login';
  }
}

Token Revocation

Understanding when and how to revoke tokens is crucial for security and user experience:

Token Revocation Policies

Login Flow Tokens
OAuth Flow Tokens
Revocation Decision Tree

Standard Login Access TokensLogin access tokens from POST /v1/auth/login are short-lived and irrevocable:

Key Points:

Access tokens expire after 6 hours automatically
No explicit revocation needed on login failure
Tokens naturally expire if not used
Cannot be refreshed - user must re-authenticate

When OTP Fails:

// OTP failure scenario
const loginResponse = await login(email, password);

if (loginResponse.isOtpRequired) {
  await sendOtp(loginResponse.userId);

  // User enters wrong OTP
  try {
    await loginWithOtp(email, password, wrongOtp);
  } catch (error) {
    // ✅ You can retry with the same credentials
    // No need to revoke anything
    const newOtp = await promptUserForNewOtp();
    await loginWithOtp(email, password, newOtp);
  }
}

Best Practice:

Allow multiple OTP retry attempts
No revocation necessary - tokens expire naturally
Clear tokens from local storage on user logout only

OAuth Access and Refresh TokensOAuth tokens should be explicitly revoked in specific scenarios:

When to Revoke OAuth Tokens:

User explicitly logs out
User revokes app access via settings
Security incident detected
App uninstall or data clear

When NOT to Revoke:

// ❌ DON'T revoke on OTP failure during OAuth flow
const oauthResponse = await completeOAuthFlow();

if (oauthResponse.isOtpRequired) {
  // OTP fails - just retry, don't revoke
  try {
    await verifyOtp(otp);
  } catch (error) {
    // ✅ Retry without revoking
    await verifyOtp(newOtp);
  }
}

When TO Revoke:

// ✅ DO revoke on explicit logout
async function logout() {
  await revokeOAuthTokens();  // Explicit revocation
  await clearLocalTokens();
  redirectToLogin();
}

// ✅ DO revoke on security events
async function handleSecurityEvent() {
  await revokeOAuthTokens();
  await notifyUser('Your session has been terminated for security reasons');
}

Use this decision tree to determine if revocation is needed:

┌─ Login Flow?
│
├─ YES → No revocation needed
│         - Tokens expire in 6 hours
│         - OTP failures: just retry
│         - Login failures: tokens never valid
│
└─ NO (OAuth Flow) → Check scenario:
    │
    ├─ User clicking "Logout"? → ✅ REVOKE
    ├─ User revoking app access? → ✅ REVOKE
    ├─ Security incident? → ✅ REVOKE
    ├─ OTP failure? → ❌ DON'T REVOKE (retry)
     ├─ Successful token issued? → ❌ DON'T REVOKE (use it)
     └─ Token refresh? → ❌ DON'T REVOKE (normal flow)

OAuth Token Revocation Implementation

Revoke OAuth tokens when users log out or revoke app access:

async function revokeAccess() {
  const accessToken = await secureStorage.get('access_token');

  try {
    await fetch('https://api.example.com/v1/auth/oauth/revoke', {
      method: 'DELETE',
      headers: {
        'Authorization': `Bearer ${accessToken}`,
        'x-client-key': process.env.CLIENT_KEY!
      }
    });
  } finally {
    // Always clear local tokens, even if API call fails
    await secureStorage.remove('access_token');
    await secureStorage.remove('refresh_token');
    await secureStorage.remove('token_expiry');
  }
}

// Example: Logout with proper revocation
async function logout() {
  try {
    await revokeAccess();
  } catch (error) {
    console.error('Revocation failed, but continuing logout:', error);
  } finally {
    // Always clear local state, even if revocation fails
    await clearAllTokens();
    redirectToLogin();
  }
}

Revocation Response

Success:

{
  "success": true,
  "message": "Tokens revoked successfully"
}

Failure Scenarios:

// Token already expired or invalid
{
  "error": "invalid_token",
  "message": "Token is already invalid"
}

// Token not found
{
  "error": "not_found",
  "message": "No active tokens found for this user"
}

Effect of OAuth Revocation: Both access and refresh tokens become invalid immediately. Users must complete the OAuth flow again to regain access.

Best Practices for Token Revocation

Always Clear Local Storage

Even if the API revocation call fails, always clear tokens from local storage to prevent unauthorized access.

try {
  await revokeAccess();
} finally {
  await clearAllTokens();  // Always execute
}

Handle Revocation Failures Gracefully

Network issues shouldn’t block logout. Log the error and continue.

try {
  await revokeAccess();
} catch (error) {
  logError('Revocation failed', error);
  // Continue logout anyway
}

Don't Revoke on Retry Scenarios

Failed OTP or temporary errors should allow retry without revocation.

// ❌ Wrong
if (otpFailed) {
  await revokeTokens();  // Don't do this
}

// ✅ Correct
if (otpFailed) {
  await promptForNewOtp();  // Just retry
}

Revoke on Security Events

Immediately revoke tokens when security issues are detected.

if (suspiciousActivity) {
  await revokeAccess();
  await notifySecurityTeam();
  await alertUser();
}

Best Practices

1. Proactive Refresh

Refresh Before Expiry

Don’t wait for a 401 error. Refresh tokens 60 seconds before they expire to ensure uninterrupted service.

if (Date.now() >= (tokenExpiry - 60000)) {
  await refreshAccessToken();
}

2. Race Condition Prevention

Prevent Concurrent Refreshes

Use locks or flags to prevent multiple simultaneous refresh requests.

private isRefreshing = false;
private refreshPromise: Promise<string> | null = null;

async refreshAccessToken() {
  if (this.isRefreshing) {
    return this.refreshPromise!;
  }
  this.isRefreshing = true;
  // ... refresh logic
}

3. Secure Storage

Use Platform Secure Storage

Never store tokens in:

localStorage (web)
AsyncStorage (React Native)
Plain SharedPreferences (Android)
UserDefaults (iOS)

Always use:

HTTP-only cookies (web)
SecureStore (React Native)
Keychain (iOS)
EncryptedSharedPreferences (Android)

OWASP Guidance: Review OWASP Session Management Cheat Sheet and OWASP HTML5 Security Cheat Sheet for comprehensive security guidance.

OWASP Security Best Practices

The following recommendations align with OWASP (Open Web Application Security Project) security standards for token storage and session management.

Web Applications

XSS Vulnerability Risk: A single Cross-Site Scripting (XSS) attack can steal ALL tokens stored in localStorage or sessionStorage. These storage mechanisms are always accessible to JavaScript running on your page.

HTTP-only cookies provide the strongest protection against XSS attacks:

// Server-side: Express.js example
app.post('/auth/callback', async (req, res) => {
  const tokens = await exchangeCodeForTokens(req.query.code);

  res.cookie('access_token', tokens.access_token, {
    httpOnly: true,        // Prevents JavaScript access
    secure: true,          // HTTPS only
    sameSite: 'strict',    // CSRF protection
    maxAge: 6 * 60 * 60 * 1000,  // 6 hours
    domain: '.yourdomain.com',   // Narrow domain scope
    path: '/api'           // Narrow path scope
  });

  res.cookie('refresh_token', tokens.refresh_token, {
    httpOnly: true,
    secure: true,
    sameSite: 'strict',
    maxAge: 7 * 24 * 60 * 60 * 1000,  // 7 days
    domain: '.yourdomain.com',
    path: '/api/auth/refresh'  // Even narrower path
  });

  res.redirect('/dashboard');
});

// Client-side: Cookies sent automatically
fetch('/api/users/me', {
  credentials: 'include'  // Include cookies in request
});

OWASP Cookie Security Attributes:

Attribute	Purpose	Required
`HttpOnly`	Prevents JavaScript from reading the cookie (XSS protection)	✅ Yes
`Secure`	Cookie only sent over HTTPS connections	✅ Yes
`SameSite=Strict`	Prevents CSRF attacks by blocking cross-site cookie transmission	✅ Yes
`Domain`	Limit cookie to specific domain (narrow scope)	✅ Yes
`Path`	Limit cookie to specific path (narrow scope)	✅ Yes
`Max-Age`	Cookie expiration time in seconds	✅ Yes

SameSite Options:

Strict: Cookie never sent on cross-site requests (most secure)
Lax: Cookie sent on top-level navigation (GET requests)
None: Cookie sent on all requests (requires Secure flag)

Memory Storage (Alternative for SPAs)

For Single-Page Applications where cookies aren’t feasible, use in-memory storage:

class SecureTokenManager {
  private accessToken: string | null = null;
  private refreshToken: string | null = null;
  private tokenExpiry: number | null = null;

  setTokens(access: string, refresh: string, expiresIn: number) {
    this.accessToken = access;
    this.refreshToken = refresh;
    this.tokenExpiry = Date.now() + (expiresIn * 1000);
  }

  getAccessToken(): string | null {
    if (this.isExpired()) {
      return null;
    }
    return this.accessToken;
  }

  getRefreshToken(): string | null {
    return this.refreshToken;
  }

  clearTokens() {
    this.accessToken = null;
    this.refreshToken = null;
    this.tokenExpiry = null;
  }

  private isExpired(): boolean {
    if (!this.tokenExpiry) return true;
    return Date.now() >= (this.tokenExpiry - 60000);
  }
}

const tokenManager = new SecureTokenManager();

Memory Storage Limitation: Tokens are lost on page refresh. You’ll need to implement a refresh mechanism or use short-lived sessions. This trade-off prioritizes security over convenience.

localStorage: Last Resort Only

⚠️ Use Only If Absolutely Necessary: localStorage should be avoided for token storage. If you must use it, implement these additional protections:

class LocalStorageTokenManager {
  private readonly ACCESS_TOKEN_KEY = 'app_access_token';
  private readonly REFRESH_TOKEN_KEY = 'app_refresh_token';

  async setTokens(access: string, refresh: string) {
    // Encrypt before storing
    const encryptedAccess = await this.encrypt(access);
    const encryptedRefresh = await this.encrypt(refresh);

    localStorage.setItem(this.ACCESS_TOKEN_KEY, encryptedAccess);
    localStorage.setItem(this.REFRESH_TOKEN_KEY, encryptedRefresh);
  }

  async getAccessToken(): Promise<string | null> {
    const encrypted = localStorage.getItem(this.ACCESS_TOKEN_KEY);
    if (!encrypted) return null;

    return await this.decrypt(encrypted);
  }

  private async encrypt(data: string): Promise<string> {
    const encoder = new TextEncoder();
    const dataBuffer = encoder.encode(data);

    const key = await this.getEncryptionKey();
    const iv = crypto.getRandomValues(new Uint8Array(12));

    const encrypted = await crypto.subtle.encrypt(
      { name: 'AES-GCM', iv },
      key,
      dataBuffer
    );

    const combined = new Uint8Array(iv.length + encrypted.byteLength);
    combined.set(iv);
    combined.set(new Uint8Array(encrypted), iv.length);

    return btoa(String.fromCharCode(...combined));
  }

  private async decrypt(data: string): Promise<string> {
    const combined = Uint8Array.from(atob(data), c => c.charCodeAt(0));
    const iv = combined.slice(0, 12);
    const encrypted = combined.slice(12);

    const key = await this.getEncryptionKey();

    const decrypted = await crypto.subtle.decrypt(
      { name: 'AES-GCM', iv },
      key,
      encrypted
    );

    const decoder = new TextDecoder();
    return decoder.decode(decrypted);
  }

  private async getEncryptionKey(): Promise<CryptoKey> {
    // In production, derive from secure source
    // This is a simplified example
    const keyMaterial = await crypto.subtle.importKey(
      'raw',
      new TextEncoder().encode('your-256-bit-secret-key-here!!'),
      'PBKDF2',
      false,
      ['deriveBits', 'deriveKey']
    );

    return crypto.subtle.deriveKey(
      {
        name: 'PBKDF2',
        salt: new TextEncoder().encode('your-salt'),
        iterations: 100000,
        hash: 'SHA-256'
      },
      keyMaterial,
      { name: 'AES-GCM', length: 256 },
      false,
      ['encrypt', 'decrypt']
    );
  }

  clearTokens() {
    localStorage.removeItem(this.ACCESS_TOKEN_KEY);
    localStorage.removeItem(this.REFRESH_TOKEN_KEY);
  }
}

OWASP Encryption Standards:

Use AES-256-GCM for symmetric encryption (minimum 128-bit, prefer 256-bit)
Use secure key derivation (PBKDF2, scrypt, or Argon2)
Never hardcode encryption keys
Rotate keys regularly

Mobile Applications

Mobile apps must use platform-native secure storage mechanisms to leverage hardware-backed encryption.

OWASP Mobile Top 10 - M9: Insecure data storage is one of the top mobile security risks. Never store tokens in:

AsyncStorage (React Native)
Plain SharedPreferences (Android)
UserDefaults (iOS)
Application sandboxed directories without encryption

iOS: Keychain Services

import Security
import Foundation

class KeychainTokenManager {
    private let service = "com.yourapp.tokens"

    func saveToken(_ token: String, forKey key: String) throws {
        let data = token.data(using: .utf8)!

        let query: [String: Any] = [
            kSecClass as String: kSecClassGenericPassword,
            kSecAttrService as String: service,
            kSecAttrAccount as String: key,
            kSecValueData as String: data,
            kSecAttrAccessible as String: kSecAttrAccessibleWhenUnlockedThisDeviceOnly
        ]

        // Delete any existing item
        SecItemDelete(query as CFDictionary)

        let status = SecItemAdd(query as CFDictionary, nil)
        guard status == errSecSuccess else {
            throw KeychainError.saveFailed
        }
    }

    func getToken(forKey key: String) throws -> String? {
        let query: [String: Any] = [
            kSecClass as String: kSecClassGenericPassword,
            kSecAttrService as String: service,
            kSecAttrAccount as String: key,
            kSecReturnData as String: true,
            kSecMatchLimit as String: kSecMatchLimitOne
        ]

        var result: AnyObject?
        let status = SecItemCopyMatching(query as CFDictionary, &result)

        guard status == errSecSuccess,
              let data = result as? Data,
              let token = String(data: data, encoding: .utf8) else {
            return nil
        }

        return token
    }

    func deleteToken(forKey key: String) {
        let query: [String: Any] = [
            kSecClass as String: kSecClassGenericPassword,
            kSecAttrService as String: service,
            kSecAttrAccount as String: key
        ]

        SecItemDelete(query as CFDictionary)
    }

    func deleteAllTokens() {
        let query: [String: Any] = [
            kSecClass as String: kSecClassGenericPassword,
            kSecAttrService as String: service
        ]

        SecItemDelete(query as CFDictionary)
    }
}

// Usage
let keychainManager = KeychainTokenManager()
try keychainManager.saveToken(accessToken, forKey: "access_token")
try keychainManager.saveToken(refreshToken, forKey: "refresh_token")

iOS Keychain Accessibility Options:

Option	Description	Use Case
`kSecAttrAccessibleWhenUnlockedThisDeviceOnly`	Accessible only when device unlocked, not backed up	✅ Recommended for tokens
`kSecAttrAccessibleAfterFirstUnlockThisDeviceOnly`	Accessible after first unlock, not backed up	Background processing
`kSecAttrAccessibleWhenUnlocked`	Accessible when unlocked, backed up to iCloud	❌ Avoid (iCloud backup risk)

Android: Keystore & EncryptedSharedPreferences

import androidx.security.crypto.EncryptedSharedPreferences
import androidx.security.crypto.MasterKey
import android.content.Context

class SecureTokenStorage(context: Context) {
    private val masterKey = MasterKey.Builder(context)
        .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
        .build()

    private val sharedPreferences = EncryptedSharedPreferences.create(
        context,
        "secure_token_prefs",
        masterKey,
        EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
        EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
    )

    fun saveTokens(accessToken: String, refreshToken: String) {
        sharedPreferences.edit().apply {
            putString("access_token", accessToken)
            putString("refresh_token", refreshToken)
            putLong("token_saved_at", System.currentTimeMillis())
            apply()
        }
    }

    fun getAccessToken(): String? {
        return sharedPreferences.getString("access_token", null)
    }

    fun getRefreshToken(): String? {
        return sharedPreferences.getString("refresh_token", null)
    }

    fun deleteAllTokens() {
        sharedPreferences.edit().clear().apply()
    }

    fun isTokenExpired(expirySeconds: Long): Boolean {
        val savedAt = sharedPreferences.getLong("token_saved_at", 0)
        val currentTime = System.currentTimeMillis()
        val elapsed = (currentTime - savedAt) / 1000
        return elapsed >= (expirySeconds - 60)
    }
}

// Usage
val storage = SecureTokenStorage(context)
storage.saveTokens(accessToken, refreshToken)

Android Security Features:

Hardware-Backed Keystore: Keys stored in Trusted Execution Environment (TEE) or Secure Element
AES-256-GCM Encryption: Industry-standard authenticated encryption
Key Derivation: EncryptedSharedPreferences handles key generation and rotation
Biometric Binding: Optional binding to device biometrics

Additional Security Measures

Transport Security

HTTPS Everywhere

Always use HTTPS for token transmission
Implement certificate pinning for mobile apps
Validate SSL/TLS certificates
Use TLS 1.2 or higher

const API_BASE = 'https://api.example.com'; // Never HTTP

fetch(API_BASE + '/endpoint', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${token}`
  }
});

Token Binding

Additional Context ValidationBind tokens to additional user context:

Device fingerprint
IP address (with caution)
User-Agent string
Geolocation (for high-risk operations)

const deviceFingerprint = await generateFingerprint();

await fetch('/api/sensitive-operation', {
  headers: {
    'Authorization': `Bearer ${token}`,
    'X-Device-Fingerprint': deviceFingerprint
  }
});

Token Rotation

Regular Token Rotation

Refresh tokens before expiry
Rotate refresh tokens on each use
Implement token versioning
Revoke old tokens immediately

const tokens = await refreshToken(oldRefreshToken);

// New refresh token returned
await storage.save('refresh_token', tokens.refresh_token);

// Old token now invalid

Logging & Monitoring

Security Event LoggingLog security-relevant events:

Token issuance
Token refresh attempts
Failed authentication
Token revocation
Unusual access patterns

logger.info('Token refreshed', {
  userId: user.id,
  timestamp: new Date().toISOString(),
  ipAddress: req.ip,
  userAgent: req.headers['user-agent']
});

OWASP Security Checklist

Use this checklist to ensure your token storage implementation follows OWASP best practices: Web Applications:

Tokens stored in HTTP-only cookies (not localStorage)
Secure flag set on all cookies (HTTPS only)
SameSite=Strict or Lax set on cookies
Narrow Domain and Path cookie attributes
Cookies expire with token lifetime
HTTPS used for entire application
XSS protection headers implemented (X-XSS-Protection, Content-Security-Policy)
Tokens never logged or exposed in URLs

Mobile Applications:

iOS: Tokens stored in Keychain with kSecAttrAccessibleWhenUnlockedThisDeviceOnly
Android: Tokens stored using EncryptedSharedPreferences with AES-256-GCM
No tokens stored in AsyncStorage, SharedPreferences, or UserDefaults
Certificate pinning implemented
Root/jailbreak detection implemented
No tokens in application logs or crash reports
Tokens cleared on app uninstall or logout

General:

Access tokens short-lived (6 hours or less)
Refresh tokens limited lifetime (7 days for financial apps)
Token refresh implemented with 60-second buffer
Automatic logout on token expiry
Token revocation on logout
No tokens in version control or environment files
Encryption keys rotated regularly
Security event logging implemented

Compliance Note: For applications handling financial data or PHI (Protected Health Information), additional requirements may apply under PCI DSS, HIPAA, or regional regulations (GDPR, CCPA).

4. Error Handling

Handle Refresh Failures Gracefully

When refresh fails, clear tokens and redirect to login:

if (response.status === 401) {
  await clearAllTokens();
  redirectToLogin();
}

5. Token Cleanup

Clear Tokens on Logout

Always clear tokens from storage when users log out:

async function logout() {
  await revokeAccess();  // API call
  await clearAllTokens();  // Local cleanup
  redirectToLogin();
}

Troubleshooting

401 Unauthorized after refresh

Cause: Refresh token expired (7 days) or was revoked.Solution:

Clear all tokens from storage
Redirect user to login
Restart OAuth flow from Step 1

if (refreshResponse.status === 401) {
  await clearAllTokens();
  window.location.href = '/login?session_expired=true';
}

Token confusion (using wrong token)

Symptom: 401 errors despite having valid tokens.Solution:

JWT Token: Only for OAuth flow (Step 3 body in API mode)
Access Token (login): Only for Step 3 Authorization header (API mode)
Access Token (final): For all subsequent API calls
Refresh Token: Only for token refresh endpoint

// CORRECT usage
// Step 3 (API mode)
headers: { 'Authorization': `Bearer ${loginAccessToken}` },
body: { token: jwtToken }

// All other API calls
headers: { 'Authorization': `Bearer ${finalAccessToken}` }

Multiple refresh requests

Cause: Race condition when multiple API calls detect expiry simultaneously.Solution:

Implement refresh lock/flag
Return same promise for concurrent refresh calls
Queue API calls during refresh

if (this.isRefreshing) {
  // Wait for existing refresh to complete
  await this.refreshPromise;
  return this.getToken();
}

Clock skew issues

Cause: Server and client clocks are out of sync.Solution:

Add 60-second buffer before expiry
Use server time in responses when possible
Handle 401s gracefully with automatic retry

const EXPIRY_BUFFER = 60000; // 60 seconds
if (Date.now() >= (tokenExpiry - EXPIRY_BUFFER)) {
  await refreshToken();
}

Testing Checklist

Functional Testing: Security Testing: See the comprehensive OWASP Security Checklist above for platform-specific security requirements including:

Web application cookie security
Mobile platform secure storage verification
Transport security and encryption
Compliance requirements

Next Steps

Security Best Practices

Essential security guidelines for production

Troubleshooting Guide

Common issues and solutions

Hosted UI Flow

Implement OAuth with hosted authentication

API Mode Flow

Implement OAuth with custom UI

Getting Started

OAuth 2.0 & Authentication

User Management

Wallet Management

Non-Custodial Wallet Delegation

Card Operations

​Overview

​Token Types

JWT Token

Access Token

Refresh Token

​Token Lifecycle

​JWT Token (OAuth Session)

​Purpose

​Characteristics

​Usage Example

​Expiration Handling

​Access Token (API Authentication)

​Purpose

​Characteristics

​Usage

​Storage

​Expiration Detection

​Refresh Token (Token Renewal)

​Purpose

​Characteristics

​Step-Up Authentication for Privileged Operations

​Refresh Flow

​Automatic Refresh Strategy

​Token Revocation

​Token Revocation Policies

​OAuth Token Revocation Implementation

​Revocation Response

​Best Practices for Token Revocation

Always Clear Local Storage

Handle Revocation Failures Gracefully

Don't Revoke on Retry Scenarios

Revoke on Security Events

​Best Practices

​1. Proactive Refresh

Refresh Before Expiry

​2. Race Condition Prevention

Prevent Concurrent Refreshes

​3. Secure Storage

Use Platform Secure Storage

​OWASP Security Best Practices

​Web Applications

​Cookie-Based Storage (Recommended)

​Memory Storage (Alternative for SPAs)

​localStorage: Last Resort Only

​Mobile Applications

​iOS: Keychain Services

​Android: Keystore & EncryptedSharedPreferences

​Additional Security Measures

Transport Security

Token Binding

Token Rotation

Logging & Monitoring

​OWASP Security Checklist

​4. Error Handling

Handle Refresh Failures Gracefully

​5. Token Cleanup

Clear Tokens on Logout

​Troubleshooting

​Testing Checklist

​Next Steps

Security Best Practices

Troubleshooting Guide

Hosted UI Flow

API Mode Flow

Overview

Token Types

Token Lifecycle

JWT Token (OAuth Session)

Purpose

Characteristics

Usage Example

Expiration Handling

Access Token (API Authentication)

Purpose

Characteristics

Usage

Storage

Expiration Detection

Refresh Token (Token Renewal)

Purpose

Characteristics

Step-Up Authentication for Privileged Operations

Refresh Flow

Automatic Refresh Strategy

Token Revocation

Token Revocation Policies

OAuth Token Revocation Implementation

Revocation Response

Best Practices for Token Revocation

Best Practices

1. Proactive Refresh

2. Race Condition Prevention

3. Secure Storage

OWASP Security Best Practices

Web Applications

Cookie-Based Storage (Recommended)

Memory Storage (Alternative for SPAs)

localStorage: Last Resort Only

Mobile Applications

iOS: Keychain Services

Android: Keystore & EncryptedSharedPreferences

Additional Security Measures

OWASP Security Checklist

4. Error Handling

5. Token Cleanup

Troubleshooting

Testing Checklist

Next Steps