workers.js

addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})

async function handleRequest(request) {
  const token = request.headers.get('Authorization');
  if (!token) {
    return new Response('Unauthorized', {
      status: 401,
      statusText: 'Unauthorized'
    });
  }

  // Verify the JWT token
  const decodedToken = verifyJwtToken(token);
  if (!decodedToken) {
    return new Response('Unauthorized', {
      status: 401,
      statusText: 'Unauthorized'
    });
  }

  // Get the user ID from the decoded token
  const userId = decodedToken.sub;

  // Look up the API key for the user
  const apiKey = await getApiKeyForUser(userId);
  if (!apiKey) {
    return new Response('Unauthorized', {
      status: 401,
      statusText: 'Unauthorized'
    });
  }

  // Check if the API key in the request matches the API key for the user
  const requestApiKey = request.headers.get('X-Api-Key');
  if (requestApiKey !== apiKey) {
    return new Response('Unauthorized', {
      status: 401,
      statusText: 'Unauthorized'
    });
  }

  // Access to the API is granted, process the request
  // ...

  return new Response('API Access Granted', {
    status: 200,
    statusText: 'OK'
  });
}

function verifyJwtToken(token) {
  // Verify the JWT token using a library such as jsonwebtoken
  // ...

  return decodedToken;
}

async function getApiKeyForUser(userId) {
  // Call an API or retrieve data from a database to get the API key for the user
  // ...
async function getApiKeyForUser(userId) {
  const API_URL = `https://<YOUR_AUTH0_DOMAIN>/api/v2/users/${userId}`;
  const API_TOKEN = '<YOUR_AUTH0_API_TOKEN>';

  const response = await fetch(API_URL, {
    method: 'GET',
    headers: {
      'Authorization': `Bearer ${API_TOKEN}`
    }
  });

  if (!response.ok) {
    throw new Error(`getApiKeyForUser failed with status ${response.status}`);
  }

  const user = await response.json();

  return user['api_key'];
}
  return apiKey;
}