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Web Bot Auth is Cloudflare’s implementation of cryptographic authentication for automated web agents. It uses RFC 9421 HTTP Message Signatures to sign outgoing HTTP requests, allowing websites to verify the identity and integrity of bot traffic. By integrating Web Bot Auth with Kernel, your browser automations can cryptographically prove their identity to websites that support signature verification.

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How it works

Web Bot Auth works via a Chrome extension that intercepts all outgoing HTTP requests and adds cryptographic signature headers:
  • Signature: The RFC 9421 signature of the request
  • Signature-Input: Metadata about how the signature was created
Websites can verify these signatures against your public key to confirm the request came from your authenticated agent.

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Quick Start with Test Key

The fastest way to get started is using Cloudflare’s RFC9421 test key, which works with their test verification site.

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1. Build the extension

Use the Kernel CLI to build the Web Bot Auth extension: 
kernel extensions build-web-bot-auth --to ./web-bot-auth-ext --upload
This command:
  • Downloads Cloudflare’s web-bot-auth browser extension source
  • Builds it with the default RFC9421 test key
  • Uploads it to Kernel as web-bot-auth
The build command requires Node.js and npm to be installed on your system.

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2. Create a browser with the extension

# Create a browser with the web-bot-auth extension
kernel browsers create --extension web-bot-auth

# The command outputs the browser ID and live view URL
# Open the live view URL in your browser, then navigate to:
# https://http-message-signatures-example.research.cloudflare.com/

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3. Verify it’s working

Navigate to Cloudflare’s test site to verify your signatures are being accepted: 
https://http-message-signatures-example.research.cloudflare.com/
This site validates requests signed with the RFC9421 test key and shows whether the signature was verified successfully.

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Using Your Own Keys

For production use, you’ll want to use your own signing keys instead of the test key.

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1. Generate an Ed25519 key pair

Create a JWK file with your Ed25519 private key. The key must include both the public (x) and private (d) components:
my-key.jwk
{
  "kty": "OKP",
  "crv": "Ed25519",
  "x": "YOUR_PUBLIC_KEY_BASE64URL",
  "d": "YOUR_PRIVATE_KEY_BASE64URL"
}
See Cloudflare’s web-bot-auth documentation for tools to generate Ed25519 key pairs.

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2. Build with your key

kernel extensions build-web-bot-auth --to ./web-bot-auth-ext --key ./my-key.jwk --upload --name my-web-bot-auth

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3. Host your public key

For websites to verify your signatures, you need to host your public key at a well-known URL. Create a key directory at: 
https://yourdomain.com/.well-known/http-message-signatures-directory
The directory should contain your public keys in JWKS format: 
{
  "keys": [
    {
      "kty": "OKP",
      "crv": "Ed25519",
      "x": "YOUR_PUBLIC_KEY_BASE64URL",
      "kid": "YOUR_KEY_ID"
    }
  ],
  "purpose": "your-bot-purpose"
}

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4. Register with Cloudflare (optional)

If you want Cloudflare-protected sites to recognize your bot, you can register your key directory with Cloudflare:
  1. Log into the Cloudflare dashboard
  2. Navigate to Manage Account > Configurations
  3. Select the Bot Submission Form tab
  4. Choose Request Signature as the verification method
  5. Enter your key directory URL
See Cloudflare’s Web Bot Auth documentation for complete details.

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References