// Redirect user to GitHub auth service
function signInWithGitHub() {
  const authServiceUrl = 'https://your-auth-service.web.val.run';
  const redirectUri = encodeURIComponent(window.location.origin + '/auth-callback');
  
  window.location.href = `${authServiceUrl}/auth/signin?redirect_uri=${redirectUri}`;
}

// Handle the callback with token
function handleAuthCallback() {
  const urlParams = new URLSearchParams(window.location.search);
  const token = urlParams.get('token');
  
  if (token) {
    // Store token securely
    localStorage.setItem('auth_token', token);
    
    // Validate token and get user info
    validateToken(token);
    
    // Clean up URL
    window.history.replaceState({}, document.title, window.location.pathname);
  }
}

// Call this on page load
window.addEventListener('load', handleAuthCallback);

async function validateToken(token) {
  const authServiceUrl = 'https://your-auth-service.web.val.run';
  
  try {
    const response = await fetch(`${authServiceUrl}/auth/validate?token=${token}`);
    const data = await response.json();
    
    if (data.valid) {
      console.log('User:', data.user);
      // Update UI with user info
      updateUserInterface(data.user);
    } else {
      console.error('Invalid token:', data.error);
      // Redirect to sign in
      signInWithGitHub();
    }
  } catch (error) {
    console.error('Token validation failed:', error);
  }
}

Create val
import React, { useState, useEffect } from 'react';

const AUTH_SERVICE_URL = 'https://your-auth-service.web.val.run';

function App() {
  const [user, setUser] = useState(null);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    // Check for auth callback
    const urlParams = new URLSearchParams(window.location.search);
    const token = urlParams.get('token');
    
    if (token) {
      localStorage.setItem('auth_token', token);
      window.history.replaceState({}, document.title, window.location.pathname);
      validateToken(token);
    } else {
      // Check for existing token
      const existingToken = localStorage.getItem('auth_token');
      if (existingToken) {
        validateToken(existingToken);
      } else {
        setLoading(false);
      }
    }
  }, []);

  const validateToken = async (token) => {
    try {
      const response = await fetch(`${AUTH_SERVICE_URL}/auth/validate?token=${token}`);
      const data = await response.json();
      
      if (data.valid) {
        setUser(data.user);
      } else {
        localStorage.removeItem('auth_token');
      }
    } catch (error) {
      console.error('Token validation failed:', error);
      localStorage.removeItem('auth_token');
    } finally {
      setLoading(false);
    }
  };

  const signIn = () => {
    const redirectUri = encodeURIComponent(window.location.origin);
    window.location.href = `${AUTH_SERVICE_URL}/auth/signin?redirect_uri=${redirectUri}`;
  };

  const signOut = () => {
    localStorage.removeItem('auth_token');
    setUser(null);
  };

  if (loading) {
    return <div>Loading...</div>;
  }

  return (
    <div>
      {user ? (
        <div>
          <h1>Welcome, {user.name || user.login}!</h1>
          <img src={user.avatar_url} alt="Avatar" width="50" height="50" />
          <button onClick={signOut}>Sign Out</button>
        </div>
      ) : (
        <div>
          <h1>Please sign in</h1>
          <button onClick={signIn}>Sign in with GitHub</button>
        </div>
      )}
    </div>
  );
}

export default App;

const express = require('express');
const fetch = require('node-fetch');

const app = express();
const AUTH_SERVICE_URL = 'https://your-auth-service.web.val.run';

// Middleware to validate auth token
async function validateAuth(req, res, next) {
  const token = req.headers.authorization?.replace('Bearer ', '');
  
  if (!token) {
    return res.status(401).json({ error: 'No token provided' });
  }

  try {
    const response = await fetch(`${AUTH_SERVICE_URL}/auth/validate?token=${token}`);
    const data = await response.json();
    
    if (data.valid) {
      req.user = data.user;
      next();
    } else {
      res.status(401).json({ error: 'Invalid token' });
    }
  } catch (error) {
    res.status(500).json({ error: 'Token validation failed' });
  }
}

// Protected route
app.get('/api/profile', validateAuth, (req, res) => {
  res.json({ user: req.user });
});

app.listen(3000);

1. Token Storage: Store tokens securely (httpOnly cookies for web apps)
2. Token Validation: Always validate tokens on the server side for protected routes
3. HTTPS Only: Only use this service over HTTPS in production
4. Token Expiry: Tokens expire after 7 days - implement refresh logic
5. Environment Variables: Never expose your GitHub client secret

// Handle common errors
async function handleAuthError(error) {
  if (error.message.includes('Invalid token')) {
    // Token expired or invalid - redirect to sign in
    localStorage.removeItem('auth_token');
    signInWithGitHub();
  } else if (error.message.includes('Network')) {
    // Network error - show retry option
    showRetryDialog();
  } else {
    // Other errors
    console.error('Auth error:', error);
  }
}