Agent card key material

What this check verifies

The Signature Agent Card is optional metadata describing the agent behind a Web Bot Auth deployment, defined in the web-bot-auth registry draft (draft-meunier-webbotauth-registry-03). It is separate from the JWKS directory and has no fixed well-known path.

A card provides key material in one of two ways (sections 3.1.2 and 3.1.3):

1. jwks_uri: the https URL of a JSON Web Key Set (RFC 7517) with the agent’s public keys.
2. jwks: the key set inline in the card. Cards in the older registry-02 shape used an inline keys member, which the checker also accepts.

The check grades the card like this:

• jwks_uri and jwks together: fail. The draft says a card MUST NOT contain both, and clients should reject such a card.
• jwks_uri with an https:// URL: pass.
• jwks_uri with another scheme: warning, because the draft requires https.
• Only inline keys (jwks, or registry-02 keys): pass.
• No key material at all: warning.

This check is advisory, as are all card checks. A failure or warning lowers the score slightly but never caps the grade and never changes the verdict. A directory with valid keys is VALID even with no card at all.

Why it matters

The card describes the agent; its key material ties that description to the keys that prove a request came from it. A verifier that reaches the card through a Signature-Agent member of type=cimd takes the keys from jwks_uri, or from jwks when there is no jwks_uri (registry-03, section 4.1). A card with both is ambiguous, which is why the draft forbids it.

For a domain check, signatures are still verified against the published directory, so for this checker the field links the card to the keys rather than replacing the directory.

How to fix it

Point jwks_uri at the key set the agent signs with, usually your directory:

{ "jwks_uri": "https://example.com/.well-known/http-message-signatures-directory" }

If you carry the keys inline as jwks instead, remove jwks_uri. Keep one of the two, and make it the key set the agent actually signs with.

References

• RFC 7517 defines the JSON Web Key Set.
• The web-bot-auth registry draft (draft-meunier-webbotauth-registry-03) defines jwks_uri (section 3.1.2), jwks (section 3.1.3), and how a client obtains keys from a card (section 4.1).
• What is a Signature Agent Card? explains the card and how it differs from an A2A or MCP agent card.
• How grading works explains why card checks are advisory.