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Serve private images

You can serve private images by using signed URL tokens. When an image requires a signed URL, the image cannot be accessed without a token unless it is being requested for a variant set to always allow public access.

  1. Log in to the Cloudflare dashboard ↗ and select your account.
  2. Select Images > Keys.
  3. Copy your key and use it to generate an expiring tokenized URL.

The example below uses a Worker that takes in a regular URL without a signed token and returns a tokenized URL that expires after one day. You can, however, set this expiration period to whatever you need, by changing the const EXPIRATION value.

const KEY = 'YOUR_KEY_FROM_IMAGES_DASHBOARD';
const EXPIRATION = 60 * 60 * 24; // 1 day


const bufferToHex = buffer =>
  [...new Uint8Array(buffer)].map(x => x.toString(16).padStart(2, '0')).join('');


async function generateSignedUrl(url) {
  // `url` is a full imagedelivery.net URL
  // e.g. https://imagedelivery.net/cheeW4oKsx5ljh8e8BoL2A/bc27a117-9509-446b-8c69-c81bfeac0a01/mobile


  const encoder = new TextEncoder();
  const secretKeyData = encoder.encode(KEY);
  const key = await crypto.subtle.importKey(
    'raw',
    secretKeyData,
    { name: 'HMAC', hash: 'SHA-256' },
    false,
    ['sign']
  );


  // Attach the expiration value to the `url`
  const expiry = Math.floor(Date.now() / 1000) + EXPIRATION;
  url.searchParams.set('exp', expiry);
  // `url` now looks like
  // https://imagedelivery.net/cheeW4oKsx5ljh8e8BoL2A/bc27a117-9509-446b-8c69-c81bfeac0a01/mobile?exp=1631289275


  const stringToSign = url.pathname + '?' + url.searchParams.toString();
  // for example, /cheeW4oKsx5ljh8e8BoL2A/bc27a117-9509-446b-8c69-c81bfeac0a01/mobile?exp=1631289275


  // Generate the signature
  const mac = await crypto.subtle.sign('HMAC', key, encoder.encode(stringToSign));
  const sig = bufferToHex(new Uint8Array(mac).buffer);


  // And attach it to the `url`
  url.searchParams.set('sig', sig);


  return new Response(url);
}


export default {
  async fetch(request, env, ctx): Promise<Response> {
    const url = new URL(event.request.url);
    const imageDeliveryURL = new URL(
      url.pathname.slice(1).replace('https:/imagedelivery.net', 'https://imagedelivery.net')
    );
    return generateSignedUrl(imageDeliveryURL);
  },
} satisfies ExportedHandler<Env>;
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