Module passkeys

Expand description

Passkeys (kernel spec §3.2, plan 3c): WebAuthn with webauthn-rs.

The relying party is public_url (decision 1): its host is the RP id and its origin the one origin accepted, with no subdomain and no other port. A public_url whose host is an IP address has no RP id, so passkeys are unavailable there.
The user handle is derived from the owner’s id (decision 3), not stored: an authenticator keeps it, and it names no one.
Ceremonies live in memory (decision 5, kernel spec §3.2), keyed by a random id: each is taken once, whatever its finish then finds, and lives at most CEREMONY_TTL_SECS. A restart drops them all; the browser starts again.
Passkeys add to the password (decision 2): registering one needs a stepped-up session (decision 7), and removing one always leaves the password. Every query names the owner (kernel spec §1).

Structs§

Ceremonies: The live ceremonies (decision 5).
PasskeyRecord: One of the owner’s passkeys, as Settings lists them (kernel spec §3.2).

Ceremony: A ceremony begun and not yet finished: what it is for, and the state webauthn-rs checks its finish against.
Refused: Why a finish was refused. Nothing changed.
Start: The outcome of starting a ceremony.

CEREMONY_TTL_SECS: How long a ceremony may take from its start to its finish, and the timeout the browser is given (decision 5).
MAX_LABEL_CHARS: The longest label a passkey takes, in characters.
MAX_LOGIN_CEREMONIES: At most this many login ceremonies are live at once, and as many registrations and step-ups: two pools, so a flood of unauthenticated login starts never pushes out a signed-in session’s ceremony (decision 5; 3c review, O1).
MAX_SESSION_CEREMONIES

counter_moves_on: Whether an authenticator’s signature counter sent may follow stored, the one last accepted (decision 6): it must move on, unless both are 0, as they stay for an authenticator with no counter (synced passkeys). One that does not may be a clone.
relying_party: The relying party for public_url: None when its host is an IP address (decision 1). Any other None is a parsed public_url that webauthn-rs refuses, unreachable as PublicUrl::parse stands; it is logged, so passkeys never stop working unexplained.
user_handle: The owner’s WebAuthn user handle: the first 16 bytes of the SHA-256 of their id. The same owner always gets the same handle.