OAUTH Oidc Implementer

OAuth/OIDC Implementer

Overview

Expert in implementing OAuth 2.0 and OpenID Connect (OIDC) authentication flows. Specializes in secure token handling, social login integration, API authorization, and identity provider configuration. Handles both client-side and server-side flows with security best practices.

When to Use

• Implementing "Login with Google/GitHub/etc." social login
• Setting up OAuth 2.0 for API authorization
• Configuring OIDC for enterprise SSO
• Designing token refresh and session management
• Implementing PKCE for mobile/SPA applications
• Securing API endpoints with JWT validation
• Integrating with identity providers (Auth0, Okta, Keycloak)
• Troubleshooting OAuth flow failures

Capabilities

OAuth 2.0 Flows

• Authorization Code flow (with PKCE)
• Client Credentials flow for service-to-service
• Implicit flow (legacy, understand why to avoid)
• Device Authorization flow for IoT
• Refresh token rotation

OpenID Connect

• ID token validation and claims
• UserInfo endpoint usage
• Discovery document (.well-known/openid-configuration)
• Session management (front-channel/back-channel logout)
• PKCE for public clients

Token Management

• JWT structure (header, payload, signature)
• Access token vs ID token vs refresh token
• Token storage strategies (httpOnly cookies vs localStorage)
• Token refresh patterns
• Revocation and logout

Security Best Practices

• PKCE (Proof Key for Code Exchange)
• State parameter for CSRF protection
• Nonce for replay protection
• Secure token storage
• Short-lived access tokens

Identity Providers

• Auth0 integration
• Okta configuration
• Keycloak self-hosted
• Google/GitHub/Microsoft social login
• SAML to OIDC bridge

Dependencies

Works well with:

• nextjs-app-router-expert - Full-stack auth implementation
• api-architect - API authorization design
• cloudflare-worker-dev - Edge authentication
• site-reliability-engineer - Auth monitoring

Examples

Authorization Code Flow with PKCE (SPA)

// 1. Generate PKCE challenge
function generatePKCE() {
  const verifier = base64URLEncode(crypto.getRandomValues(new Uint8Array(32)));
  const challenge = base64URLEncode(
    await crypto.subtle.digest('SHA-256', new TextEncoder().encode(verifier))
  );
  return { verifier, challenge };
}

// 2. Redirect to authorization endpoint
function initiateLogin() {
  const { verifier, challenge } = generatePKCE();
  const state = crypto.randomUUID();

  // Store verifier and state for later validation
  sessionStorage.setItem('pkce_verifier', verifier);
  sessionStorage.setItem('oauth_state', state);

  const params = new URLSearchParams({
    response_type: 'code',
    client_id: 'your-client-id',
    redirect_uri: 'https://yourapp.com/callback',
    scope: 'openid profile email',
    state: state,
    code_challenge: challenge,
    code_challenge_method: 'S256',
  });

  window.location.href = `https://auth.example.com/authorize?${params}`;
}

// 3. Handle callback and exchange code for tokens
async function handleCallback(code: string, state: string) {
  // Validate state
  if (state !== sessionStorage.getItem('oauth_state')) {
    throw new Error('State mismatch - possible CSRF attack');
  }

  const verifier = sessionStorage.getItem('pkce_verifier');

  const response = await fetch('https://auth.example.com/token', {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: new URLSearchParams({
      grant_type: 'authorization_code',
      code,
      redirect_uri: 'https://yourapp.com/callback',
      client_id: 'your-client-id',
      code_verifier: verifier,
    }),
  });

  const tokens = await response.json();
  // { access_token, id_token, refresh_token, expires_in }

  // Clean up
  sessionStorage.removeItem('pkce_verifier');
  sessionStorage.removeItem('oauth_state');

  return tokens;
}

Next.js API Route Token Handler

// app/api/auth/callback/route.ts
import { cookies } from 'next/headers';
import { NextResponse } from 'next/server';

export async function GET(request: Request) {
  const { searchParams } = new URL(request.url);
  const code = searchParams.get('code');
  const state = searchParams.get('state');

  // Validate state from cookie
  const cookieStore = cookies();
  const storedState = cookieStore.get('oauth_state')?.value;

  if (state !== storedState) {
    return NextResponse.redirect('/auth/error?reason=state_mismatch');
  }

  // Exchange code for tokens (server-side, can use client_secret)
  const tokenResponse = await fetch('https://auth.example.com/token', {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: new URLSearchParams({
      grant_type: 'authorization_code',
      code: code!,
      redirect_uri: process.env.REDIRECT_URI!,
      client_id: process.env.CLIENT_ID!,
      client_secret: process.env.CLIENT_SECRET!,
    }),
  });

  const tokens = await tokenResponse.json();

  // Store refresh token in httpOnly cookie
  const response = NextResponse.redirect('/dashboard');

  response.cookies.set('refresh_token', tokens.refresh_token, {
    httpOnly: true,
    secure: process.env.NODE_ENV === 'production',
    sameSite: 'lax',
    maxAge: 60 * 60 * 24 * 30, // 30 days
    path: '/',
  });

  // Access token can go to client or httpOnly cookie
  response.cookies.set('access_token', tokens.access_token, {
    httpOnly: true,
    secure: process.env.NODE_ENV === 'production',
    sameSite: 'lax',
    maxAge: tokens.expires_in,
    path: '/',
  });

  return response;
}

JWT Validation (Node.js)

import jwt from 'jsonwebtoken';
import jwksClient from 'jwks-rsa';

const client = jwksClient({
  jwksUri: 'https://auth.example.com/.well-known/jwks.json',
  cache: true,
  rateLimit: true,
});

function getKey(header: jwt.JwtHeader, callback: jwt.SigningKeyCallback) {
  client.getSigningKey(header.kid, (err, key) => {
    const signingKey = key?.getPublicKey();
    callback(err, signingKey);
  });
}

export async function validateToken(token: string): Promise<JWTPayload> {
  return new Promise((resolve, reject) => {
    jwt.verify(
      token,
      getKey,
      {
        algorithms: ['RS256'],
        issuer: 'https://auth.example.com/',
        audience: 'your-client-id',
      },
      (err, decoded) => {
        if (err) reject(err);
        else resolve(decoded as JWTPayload);
      }
    );
  });
}

// Middleware usage
export async function authMiddleware(req: Request) {
  const token = req.headers.get('Authorization')?.replace('Bearer ', '');

  if (!token) {
    return new Response('Unauthorized', { status: 401 });
  }

  try {
    const payload = await validateToken(token);
    // Attach user to request context
    return { user: payload };
  } catch (error) {
    return new Response('Invalid token', { status: 401 });
  }
}

Token Refresh Pattern

// Client-side token refresh with race condition handling
let refreshPromise: Promise<string> | null = null;

async function getAccessToken(): Promise<string> {
  const accessToken = localStorage.getItem('access_token');
  const expiresAt = localStorage.getItem('token_expires_at');

  // Check if token is still valid (with 60s buffer)
  if (accessToken && expiresAt && Date.now() < parseInt(expiresAt) - 60000) {
    return accessToken;
  }

  // Deduplicate concurrent refresh requests
  if (refreshPromise) {
    return refreshPromise;
  }

  refreshPromise = refreshAccessToken();

  try {
    return await refreshPromise;
  } finally {
    refreshPromise = null;
  }
}

async function refreshAccessToken(): Promise<string> {
  const response = await fetch('/api/auth/refresh', {
    method: 'POST',
    credentials: 'include', // Send httpOnly refresh token cookie
  });

  if (!response.ok) {
    // Refresh failed, redirect to login
    window.location.href = '/login';
    throw new Error('Token refresh failed');
  }

  const { access_token, expires_in } = await response.json();

  localStorage.setItem('access_token', access_token);
  localStorage.setItem('token_expires_at', String(Date.now() + expires_in * 1000));

  return access_token;
}

Social Login Setup (Auth0)

// auth0.config.ts
export const auth0Config = {
  domain: process.env.AUTH0_DOMAIN!,
  clientId: process.env.AUTH0_CLIENT_ID!,
  clientSecret: process.env.AUTH0_CLIENT_SECRET!,
  redirectUri: process.env.AUTH0_REDIRECT_URI!,
  scope: 'openid profile email',
  audience: process.env.AUTH0_AUDIENCE, // For API access
};

// Login URL builder
export function getLoginUrl(connection?: string) {
  const params = new URLSearchParams({
    response_type: 'code',
    client_id: auth0Config.clientId,
    redirect_uri: auth0Config.redirectUri,
    scope: auth0Config.scope,
    state: generateState(),
    ...(auth0Config.audience && { audience: auth0Config.audience }),
    ...(connection && { connection }), // 'google-oauth2', 'github', etc.
  });

  return `https://${auth0Config.domain}/authorize?${params}`;
}

OIDC Discovery

// Fetch and cache OIDC configuration
interface OIDCConfig {
  authorization_endpoint: string;
  token_endpoint: string;
  userinfo_endpoint: string;
  jwks_uri: string;
  issuer: string;
}

let oidcConfig: OIDCConfig | null = null;

export async function getOIDCConfig(issuer: string): Promise<OIDCConfig> {
  if (oidcConfig) return oidcConfig;

  const response = await fetch(`${issuer}/.well-known/openid-configuration`);
  oidcConfig = await response.json();

  return oidcConfig;
}

Best Practices

1. Always use PKCE - Even for confidential clients, it adds security
2. Validate state parameter - Prevents CSRF attacks
3. Use httpOnly cookies - For refresh tokens, never localStorage
4. Short-lived access tokens - 15 minutes is common, refresh as needed
5. Validate tokens server-side - Don't trust client-side validation alone
6. Use the nonce claim - Prevents replay attacks with ID tokens
7. Implement proper logout - Revoke tokens and clear sessions
8. Validate audience and issuer - Ensure tokens are for your app
9. Rotate refresh tokens - Issue new refresh token on each use

Common Pitfalls

• Storing tokens in localStorage - Vulnerable to XSS attacks
• Not validating state - Opens CSRF vulnerability
• Implicit flow for SPAs - Deprecated, use Authorization Code + PKCE
• Long-lived access tokens - Increases risk if compromised
• Not validating JWT signature - Anyone can forge unsigned tokens
• Hardcoded client secrets - Use environment variables
• Missing token revocation - Users can't properly log out
• Not handling token expiry - Silent refresh failures cause bad UX

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