Note

This example Worker makes use of the [Node.js Buffer API](https://developers.cloudflare.com/workers/runtime-apis/nodejs/buffer/), which is available as part of the Worker's runtime [Node.js compatibility mode](https://developers.cloudflare.com/workers/runtime-apis/nodejs/). To run this Worker, you will need to [enable the `nodejs_compat` compatibility flag](https://developers.cloudflare.com/workers/runtime-apis/nodejs/#get-started).

You can both verify and generate signed requests from within a Worker using the [Web Crypto APIs](https://developer.mozilla.org/en-US/docs/Web/API/Crypto/subtle).

The following Worker will:

* For request URLs beginning with `/generate/`, replace `/generate/` with `/`, sign the resulting path with its timestamp, and return the full, signed URL in the response body.

* For all other request URLs, verify the signed URL and allow the request through.

- JavaScript

  ```js
  import { Buffer } from "node:buffer";


  const encoder = new TextEncoder();


  // How long an HMAC token should be valid for, in seconds
  const EXPIRY = 60;


  export default {
    /**
     *
     * @param {Request} request
     * @param {{SECRET_DATA: string}} env
     * @returns
     */
    async fetch(request, env) {
      // You will need some secret data to use as a symmetric key. This should be
      // attached to your Worker as an encrypted secret.
      // Refer to https://developers.cloudflare.com/workers/configuration/secrets/
      const secretKeyData = encoder.encode(
        env.SECRET_DATA ?? "my secret symmetric key",
      );


      // Import your secret as a CryptoKey for both 'sign' and 'verify' operations
      const key = await crypto.subtle.importKey(
        "raw",
        secretKeyData,
        { name: "HMAC", hash: "SHA-256" },
        false,
        ["sign", "verify"],
      );


      const url = new URL(request.url);


      // This is a demonstration Worker that allows unauthenticated access to /generate
      // In a real application you would want to make sure that
      // users could only generate signed URLs when authenticated
      if (url.pathname.startsWith("/generate/")) {
        url.pathname = url.pathname.replace("/generate/", "/");


        const timestamp = Math.floor(Date.now() / 1000);


        // This contains all the data about the request that you want to be able to verify
        // Here we only sign the timestamp and the pathname, but often you will want to
        // include more data (for instance, the URL hostname or query parameters)
        const dataToAuthenticate = `${url.pathname}${timestamp}`;


        const mac = await crypto.subtle.sign(
          "HMAC",
          key,
          encoder.encode(dataToAuthenticate),
        );


        // Refer to https://developers.cloudflare.com/workers/runtime-apis/nodejs/
        // for more details on using Node.js APIs in Workers
        const base64Mac = Buffer.from(mac).toString("base64");


        url.searchParams.set("verify", `${timestamp}-${base64Mac}`);


        return new Response(`${url.pathname}${url.search}`);
        // Verify all non /generate requests
      } else {
        // Make sure you have the minimum necessary query parameters.
        if (!url.searchParams.has("verify")) {
          return new Response("Missing query parameter", { status: 403 });
        }


        const [timestamp, hmac] = url.searchParams.get("verify").split("-");


        const assertedTimestamp = Number(timestamp);


        const dataToAuthenticate = `${url.pathname}${assertedTimestamp}`;


        const receivedMac = Buffer.from(hmac, "base64");


        // Use crypto.subtle.verify() to guard against timing attacks. Since HMACs use
        // symmetric keys, you could implement this by calling crypto.subtle.sign() and
        // then doing a string comparison -- this is insecure, as string comparisons
        // bail out on the first mismatch, which leaks information to potential
        // attackers.
        const verified = await crypto.subtle.verify(
          "HMAC",
          key,
          receivedMac,
          encoder.encode(dataToAuthenticate),
        );


        if (!verified) {
          return new Response("Invalid MAC", { status: 403 });
        }


        // Signed requests expire after one minute. Note that this value should depend on your specific use case
        if (Date.now() / 1000 > assertedTimestamp + EXPIRY) {
          return new Response(
            `URL expired at ${new Date((assertedTimestamp + EXPIRY) * 1000)}`,
            { status: 403 },
          );
        }
      }


      return fetch(new URL(url.pathname, "https://example.com"), request);
    },
  };
  ```

- TypeScript

  ```ts
  import { Buffer } from "node:buffer";


  const encoder = new TextEncoder();


  // How long an HMAC token should be valid for, in seconds
  const EXPIRY = 60;


  interface Env {
    SECRET_DATA: string;
  }
  export default {
    async fetch(request, env): Promise<Response> {
      // You will need some secret data to use as a symmetric key. This should be
      // attached to your Worker as an encrypted secret.
      // Refer to https://developers.cloudflare.com/workers/configuration/secrets/
      const secretKeyData = encoder.encode(
        env.SECRET_DATA ?? "my secret symmetric key",
      );


      // Import your secret as a CryptoKey for both 'sign' and 'verify' operations
      const key = await crypto.subtle.importKey(
        "raw",
        secretKeyData,
        { name: "HMAC", hash: "SHA-256" },
        false,
        ["sign", "verify"],
      );


      const url = new URL(request.url);


      // This is a demonstration Worker that allows unauthenticated access to /generate
      // In a real application you would want to make sure that
      // users could only generate signed URLs when authenticated
      if (url.pathname.startsWith("/generate/")) {
        url.pathname = url.pathname.replace("/generate/", "/");


        const timestamp = Math.floor(Date.now() / 1000);


        // This contains all the data about the request that you want to be able to verify
        // Here we only sign the timestamp and the pathname, but often you will want to
        // include more data (for instance, the URL hostname or query parameters)
        const dataToAuthenticate = `${url.pathname}${timestamp}`;


        const mac = await crypto.subtle.sign(
          "HMAC",
          key,
          encoder.encode(dataToAuthenticate),
        );


        // Refer to https://developers.cloudflare.com/workers/runtime-apis/nodejs/
        // for more details on using NodeJS APIs in Workers
        const base64Mac = Buffer.from(mac).toString("base64");


        url.searchParams.set("verify", `${timestamp}-${base64Mac}`);


        return new Response(`${url.pathname}${url.search}`);
        // Verify all non /generate requests
      } else {
        // Make sure you have the minimum necessary query parameters.
        if (!url.searchParams.has("verify")) {
          return new Response("Missing query parameter", { status: 403 });
        }


        const [timestamp, hmac] = url.searchParams.get("verify").split("-");


        const assertedTimestamp = Number(timestamp);


        const dataToAuthenticate = `${url.pathname}${assertedTimestamp}`;


        const receivedMac = Buffer.from(hmac, "base64");


        // Use crypto.subtle.verify() to guard against timing attacks. Since HMACs use
        // symmetric keys, you could implement this by calling crypto.subtle.sign() and
        // then doing a string comparison -- this is insecure, as string comparisons
        // bail out on the first mismatch, which leaks information to potential
        // attackers.
        const verified = await crypto.subtle.verify(
          "HMAC",
          key,
          receivedMac,
          encoder.encode(dataToAuthenticate),
        );


        if (!verified) {
          return new Response("Invalid MAC", { status: 403 });
        }


        // Signed requests expire after one minute. Note that this value should depend on your specific use case
        if (Date.now() / 1000 > assertedTimestamp + EXPIRY) {
          return new Response(
            `URL expired at ${new Date((assertedTimestamp + EXPIRY) * 1000)}`,
            { status: 403 },
          );
        }
      }


      return fetch(new URL(url.pathname, "https://example.com"), request);
    },
  } satisfies ExportedHandler<Env>;
  ```

## Validate signed requests using the WAF

The provided example code for signing requests is compatible with the [`is_timed_hmac_valid_v0()`](https://developers.cloudflare.com/ruleset-engine/rules-language/functions/#hmac-validation) Rules language function. This means that you can verify requests signed by the Worker script using a [WAF custom rule](https://developers.cloudflare.com/waf/custom-rules/use-cases/configure-token-authentication/#option-2-configure-using-waf-custom-rules).
