verify_agent_signature

Neutral third-party Web Bot Auth verification. An origin — or the PDP
deciding for it — received a request from a claimed agent carrying the
Web Bot Auth headers (Signature, Signature-Input, Signature-Agent).
Relay those headers here, plus the authority the request was addressed
to, and TunnelMind verifies the Ed25519 signature against the agent's
own published key directory
(https://<agent>/.well-known/http-message-signatures-directory).

Facts, not a verdict: state: verified means "this signature
cryptographically verifies against that directory" — whether to trust
the agent behind it is your policy engine's call.

Use this tool when:

• A request claims a cryptographic agent identity (Signature-Agent

header present) and you must check the claim before serving it.

• You want signature verification independent of your CDN — or you are

not behind a CDN that implements Web Bot Auth at all.

Inputs (JSON body):

• signature (required): the received Signature header value.
• signature_input (required): the received Signature-Input header value.
• signature_agent (required): the received Signature-Agent header

value (quoted https origin).

• authority (required): the host the request was addressed to.
• method, path, scheme (optional): only needed if the signature's

covered components include them.

Returns:

• state: one of

- verified — Ed25519 signature verifies against a key in the
agent's published directory.
- invalid_signature — key found, signature does not verify
(tampered or forged).
- unknown_key — directory reachable but contains no key with the
claimed thumbprint.
- directory_unreachable — the claimed key directory did not answer;
an honest degraded state, not evidence of forgery.
- expired — the signature's expires timestamp has passed.
- malformed — headers do not parse as a Web Bot Auth signature.

• key_id: the claimed RFC 7638 JWK thumbprint.
• directory_url: the resolved well-known directory URL.
• params: created/expires/alg/tag as sent.
• checks[]: per-check {name, pass, detail} facts a PDP can gate on.

Cost:

• Counts as one request against the daily rate limit.

Latency:

• Typical: <100ms when the agent's directory is KV-cached (1h TTL);

up to ~5s on first sight of a new directory.