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Guzzle Web Bot Auth Middleware

This package signs outbound Guzzle requests with Ed25519 HTTP Message Signatures. It lets an automated client prove continuity of identity without relying only on a spoofable User-Agent, changing cloud IP ranges, or a shared secret negotiated with every origin.

The receiving server still decides whether to trust or authorize that identity. A valid signature proves control of a key published by the claimed Signature Agent; it does not prove that the bot is safe or that a request is authorized.

Standards status

The implementation follows:

• RFC 9421: HTTP Message Signatures for signature construction and fields.
• RFC 9651: Structured Field Values for HTTP, which obsoletes RFC 8941, for field serialization.
• RFC 7638 and RFC 8037 Appendix A.3 for Ed25519 JWK Thumbprints.
• draft-meunier-webbotauth-httpsig-protocol-02, published 18 August 2026, for the Web Bot Auth profile and key discovery.

RFC 9421 is stable. The Web Bot Auth protocol is an active Standards Track Internet-Draft and can change before it becomes an RFC. The exact draft revision above is therefore part of this package's compatibility contract; Renovate and the scheduled integration test help surface ecosystem drift, but consumers should still review release notes before upgrading.

For each request the middleware currently emits:

Covering the method, path, and query as well as the required authority narrows replay scope. If the request already has a Content-Digest field, the middleware covers it too. It does not calculate a digest or buffer request bodies for you.

Deployment compatibility

Cloudflare's deployed verifier and public documentation currently use the older bare-string Signature-Agent field, while the current Internet-Draft requires the dictionary form shown above. Use the standards-current directory default for new integrations. If a Cloudflare endpoint returns 400 because it has not adopted the current draft yet, select the explicit cloudflare_legacy mode as a temporary compatibility bridge:

That mode emits a bare Structured Fields string and covers "signature-agent" without the current draft's key parameter. It is intentionally opt-in and should be removed from application configuration when the target verifier supports the current draft.

Requirements

• PHP 7.4 or later with ext-sodium.
• Guzzle 7 or 8.

Installation

Generate an Ed25519 key

From your application root:

The script creates:

• ed25519_private.key, mode 0600, containing the base64-encoded private key. It is deliberately not printed; keep it out of source control and backups that are not approved for secrets.
• ed25519_public.key, containing the base64-encoded public key.
• A public JWK and its unpadded base64url SHA-256 thumbprint (kid). The JWK uses the HTTP Message Signatures algorithm name ed25519.

To convert an existing raw 32-byte Ed25519 public key encoded as base64:

Publish the key directory

With the default directory discovery type, publish a JWKS at:

Serve it over HTTPS with Content-Type: application/http-message-signatures-directory+json:

The current draft permits a directly resolved directory without a signed directory response. A signature is still needed when redistributed key material is expected to prove its association with the directory URL. This package signs requests; serving and signing the directory response remains the operator's responsibility.

Usage

Pass the private key or its file path, the JWK Thumbprint, and the Signature Agent origin:

The exact legacy well-known URL is also accepted and normalized to its origin, so existing configuration can migrate without changing the stored value.

Discovery types and optional settings

Constructor arguments after the three required values are intentionally optional and retain their original positions:

1. tag defaults to web-bot-auth. A custom value is retained for backwards compatibility but opts the signature out of the Web Bot Auth profile.
2. expiresInSeconds defaults to 300. The draft recommends no more than 24 hours; shorter lifetimes reduce replay exposure.
3. signatureLabel defaults to sig.
4. discoveryType defaults to directory; current-draft values are directory, jwks_uri, and cimd. The transitional cloudflare_legacy value is also available for the deployed compatibility case described above.
5. clock is an optional callable for deterministic testing and must return an integer Unix timestamp.

For a direct JWKS URL, select jwks_uri explicitly:

This emits Signature-Agent: sig="https://agent.example/keys.json";type=jwks_uri as required by the current draft.

Upgrading from 1.x

Version 2.0 corrects the RFC 9421 wire format and adopts the current dictionary form of Signature-Agent. This is intentionally a major release because verifiers or tests that depended on the old malformed/legacy fields will observe different headers.

The constructor's first five positional arguments remain compatible. The default signature label also remains sig. The material changes are:

• Signature is now a Structured Fields Byte Sequence (sig=:...:).
• Signature-Input is now a valid parameterized Inner List.
• Signature-Agent is a dictionary keyed to the covered signature label.
• The default directory identity is the HTTPS origin; the well-known path is resolved by the verifier.
• keyid is validated as the JWK Thumbprint required by the profile.
• keyid must match the configured private key, so key-pair configuration mistakes now fail immediately.
• Method, path, and query are covered to reduce replay scope.

If a 1.x application targets Cloudflare's currently deployed legacy verifier, migrate it with cloudflare_legacy first, verify the endpoint accepts the new RFC 9421 serialization, and move to directory once that endpoint supports the current draft.

Development

The CI matrix tests PHP 7.4 through 8.5 with current dependencies, tests a Composer-resolvable low dependency set separately, runs PHPStan 2 and PHP CS Fixer, audits production dependencies, and runs the live transport integration test weekly or on demand.

Commits use Conventional Commits. Release Please turns them into a release pull request and applies Semantic Versioning: fix is patch, feat is minor, and feat! or a BREAKING CHANGE footer is major. See RELEASE.md.

Security

See SECURITY.md for private vulnerability reporting.

License

MIT. See LICENSE.MIT.