```// Function to generate a nonce (e.g., a timestamp)
function generateNonce() {
    return Date.now().toString();
}

// Function to generate HMAC signature using Web Crypto API
async function generateHMAC(nonce, apiKey, secretKey) {
    const key = await crypto.subtle.importKey(
        'raw',
        new TextEncoder().encode(secretKey),
        { name: 'HMAC', hash: 'SHA-256' },
        false,
        ['sign']
    );
    const signature = await crypto.subtle.sign(
        'HMAC',
        key,
        new TextEncoder().encode(nonce + apiKey)
    );
    return Array.from(new Uint8Array(signature))
        .map(b => b.toString(16).padStart(2, '0'))
        .join('');
}

// Main request handler
export async function onRequest(context) {
    const { request } = context;
    const url = new URL(request.url);
    const secretKey = context.env.SECRET_KEY; // Defined in the Cloudflare Workers environment
    const apiKey = context.env.API_KEY;       // Defined in the Cloudflare Workers environment
    // CORS check for allowed domains
    //if (!checkCors(url.origin)) {
    //    return new Response('CORS check failed', { status: 403 });
    //}

    // Handle /v1/signature path
    if (url.pathname === '/v1/signature') {
        const nonce = generateNonce();
        const signature = await generateHMAC(nonce, apiKey, secretKey);

        return new Response(
            JSON.stringify({
                apiKey,
                signature,
                nonce,
            })
        );
    }
    return new Response('Not Found', { status: 404 });
}

// CORS preflight handler for OPTIONS method
//async function handleOptions(context) {
//    const { request } = context;
//    const url = new URL(request.url);
//
//    if (!checkCors(url.origin)) {
//        return new Response('CORS check failed', { status: 403 });
//    }
//
//    return new Response(null, {
//        status: 204,
//        headers: {
//            'Access-Control-Allow-Origin': "*",
//            'Access-Control-Allow-Methods': 'GET, OPTIONS',
//        },
//    });
//}

// Event listener for requests
addEventListener('fetch', (event) => {
    const request = event.request;
    //if (request.method === 'OPTIONS') {
    //    event.respondWith(handleOptions(event)); // Handle preflight requests
    //} else {
    //    event.respondWith(onRequest(event)); // Handle GET and other requests
    //}
});
```