---
title: Sign requests
description: Verify a signed request using the HMAC and SHA-256 algorithms or return a 403.
image: https://developers.cloudflare.com/dev-products-preview.png
---

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# Sign requests

**Last reviewed:**  over 2 years ago 

Verify a signed request using the HMAC and SHA-256 algorithms or return a 403.

If you want to get started quickly, click on the button below.

[![Deploy to Cloudflare](https://deploy.workers.cloudflare.com/button)](https://deploy.workers.cloudflare.com/?url=https://github.com/cloudflare/docs-examples/tree/main/workers/signing-requests)

This creates a repository in your GitHub account and deploys the application to Cloudflare Workers.

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 Workers 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 ](#tab-panel-9378)
* [  TypeScript ](#tab-panel-9379)
* [  Hono ](#tab-panel-9380)
* [  Python ](#tab-panel-9381)

JavaScript

```

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

```

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>;


```

TypeScript

```

import { Buffer } from "node:buffer";

import { Hono } from "hono";

import { proxy } from "hono/proxy";


const encoder = new TextEncoder();


// How long an HMAC token should be valid for, in seconds

const EXPIRY = 60;


interface Env {

  SECRET_DATA: string;

}


const app = new Hono();


// Handle URL generation requests

app.get("/generate/*", async (c) => {

  const env = c.env;


  // You will need some secret data to use as a symmetric key

  const secretKeyData = encoder.encode(

    env.SECRET_DATA ?? "my secret symmetric key",

  );


  // Import the 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"],

  );


  // Replace "/generate/" prefix with "/"

  let pathname = c.req.path.replace("/generate/", "/");


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


  // Data to authenticate: pathname + timestamp

  const dataToAuthenticate = `${pathname}${timestamp}`;


  // Sign the data

  const mac = await crypto.subtle.sign(

    "HMAC",

    key,

    encoder.encode(dataToAuthenticate),

  );


  // Convert the signature to base64

  const base64Mac = Buffer.from(mac).toString("base64");


  // Add verification parameter to URL

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


  return c.text(`${pathname}${url.search}`);

});


// Handle verification for all other requests

app.all("*", async (c) => {

  const env = c.env;

  const url = c.req.url;


  // You will need some secret data to use as a symmetric key

  const secretKeyData = encoder.encode(

    env.SECRET_DATA ?? "my secret symmetric key",

  );


  // Import the 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"],

  );


  // Make sure the request has the verification parameter

  if (!c.req.query("verify")) {

    return c.text("Missing query parameter", 403);

  }


  // Extract timestamp and signature

  const [timestamp, hmac] = c.req.query("verify")!.split("-");

  const assertedTimestamp = Number(timestamp);


  // Recreate the data that should have been signed

  const dataToAuthenticate = `${c.req.path}${assertedTimestamp}`;


  // Convert base64 signature back to ArrayBuffer

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


  // Verify the signature

  const verified = await crypto.subtle.verify(

    "HMAC",

    key,

    receivedMac,

    encoder.encode(dataToAuthenticate),

  );


  // If verification fails, return 403

  if (!verified) {

    return c.text("Invalid MAC", 403);

  }


  // Check if the signature has expired

  if (Date.now() / 1000 > assertedTimestamp + EXPIRY) {

    return c.text(

      `URL expired at ${new Date((assertedTimestamp + EXPIRY) * 1000)}`,

      403,

    );

  }


  // If verification passes, proxy the request to example.com

  return proxy(`https://example.com/${c.req.path}`, ...c.req);

});


export default app;


```

Python

```

from workers import WorkerEntrypoint

from pyodide.ffi import to_js as _to_js

from js import Response, URL, TextEncoder, Buffer, fetch, Object, crypto


def to_js(x):

    return _to_js(x, dict_converter=Object.fromEntries)


encoder = TextEncoder.new()


# How long an HMAC token should be valid for, in seconds

EXPIRY = 60


class Default(WorkerEntrypoint):

    async def fetch(self, request):

        # Get the secret key

        secret_key_data = encoder.encode(getattr(self.env, "SECRET_DATA", None) or "my secret symmetric key")


        # Import the secret as a CryptoKey for both 'sign' and 'verify' operations

        key = await crypto.subtle.importKey(

            "raw",

            secret_key_data,

            to_js({"name": "HMAC", "hash": "SHA-256"}),

            False,

            ["sign", "verify"]

        )


        url = URL.new(request.url)


        if url.pathname.startswith("/generate/"):

            url.pathname = url.pathname.replace("/generate/", "/", 1)


            timestamp = int(Date.now() / 1000)


            # Data to authenticate

            data_to_authenticate = f"{url.pathname}{timestamp}"


            # Sign the data

            mac = await crypto.subtle.sign(

                "HMAC",

                key,

                encoder.encode(data_to_authenticate)

            )


            # Convert to base64

            base64_mac = Buffer.from(mac).toString("base64")


            # Set the verification parameter

            url.searchParams.set("verify", f"{timestamp}-{base64_mac}")


            return Response.new(f"{url.pathname}{url.search}")

        else:

            # Verify the request

            if not "verify" in url.searchParams:

                return Response.new("Missing query parameter", status=403)


            verify_param = url.searchParams.get("verify")

            timestamp, hmac = verify_param.split("-")


            asserted_timestamp = int(timestamp)


            data_to_authenticate = f"{url.pathname}{asserted_timestamp}"


            received_mac = Buffer.from(hmac, "base64")


            # Verify the signature

            verified = await crypto.subtle.verify(

                "HMAC",

                key,

                received_mac,

                encoder.encode(data_to_authenticate)

            )


            if not verified:

                return Response.new("Invalid MAC", status=403)


            # Check expiration

            if Date.now() / 1000 > asserted_timestamp + EXPIRY:

                expiry_date = Date.new((asserted_timestamp + EXPIRY) * 1000)

                return Response.new(f"URL expired at {expiry_date}", status=403)


        # Proxy to example.com if verification passes

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


```

## 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 [custom rule](https://developers.cloudflare.com/waf/custom-rules/use-cases/configure-token-authentication/#option-2-configure-using-custom-rules).

```json
{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/directory/","name":"Directory"}},{"@type":"ListItem","position":2,"item":{"@id":"/workers/","name":"Workers"}},{"@type":"ListItem","position":3,"item":{"@id":"/workers/examples/","name":"Examples"}},{"@type":"ListItem","position":4,"item":{"@id":"/workers/examples/signing-requests/","name":"Sign requests"}}]}
```