Signed receipts

Every response to an authenticated agent carries an Ed25519-signed AgentGate-Receipt. Verify it offline with the JWKS or online.

Every response to an authenticated agent (Web Bot Auth or the shared key, on the agent API and for verified browser agents on the form) carries a signed receipt of the decision:

HTTP

AgentGate-Receipt: eyJhbGciOiJFZERTQSIsInR5cCI6ImFnZW50Z2F0ZS1yZWNlaXB0K2p3dCIsImtpZCI6ImUxIn0.eyJpc3MiOi…

A receipt is signed when the status is written, so it records what the agent actually got (for example 402 or 429). A dropped request gets no receipt.

Format

A compact JWS:

Part	Content
Header	`alg` `EdDSA`, `typ` `agentgate-receipt+jwt`, `kid`
`iss`	the issuing AgentGate
`sub`	your agent
`jti`	the decision ID
`iat`	issue time
`site`, `action`, `route`	where and what
`outcome`	`allow`, `challenge`, `block`, `payment_required`, `rate_limited`, `conflict` or `error`
`status`	the HTTP status you received

A JWS was chosen over an RFC 9421 response signature because a receipt must outlive the response it describes.

Verify

Offline. Fetch /.well-known/agentgate-keys.json (a JWKS of OKP Ed25519 keys) and use any JOSE library that supports EdDSA. Check typ. In Go, VerifyReceipt(token, ParseJWKS(jwks)) is the reference verifier.
Online. POST /v1/receipts/verify with {"receipt": "…"} returns valid, the claims, and whether the decision is still in the site's log and matches (recorded, matches). The log is kept for 7 days by default.

Keys stay in the JWKS after a rotation until the operator retires them. Keep a copy of the JWKS alongside any receipts you may need to prove later.