Module session 

Session tokens, the cookie they travel in, the extractors that resolve them, the CSRF check, and the login rate limiter.

The token

32 bytes from the system CSPRNG, base64url-unpadded (43 characters, cookie- safe unquoted). Stored as hex(SHA-256(token)) and never in plaintext, so a read of the database — a backup, a .dump, an injection — yields nothing replayable. Not the password KDF: the token has 256 bits of entropy, so there is no dictionary to slow down and a slow hash would buy nothing but latency on every request. Lookup is by the hash, and the value looked up is the secret, so that path needs no constant-time comparison — unlike the CSRF token, which is compared against a caller-supplied string.

CSRF, and why SameSite=Strict is not enough

The usual answer is that SameSite covers it. It does not, here, and the reason is specific: SameSite is scoped to the registrable domain, not the origin — different ports of the same host are same-site. A panel on :3001 beside anything else on :8080 of the same box is exactly the configuration it does not protect. So there is a per-session token as well, plus an origin gate that also covers login (which by definition carries no session token yet).

Enforcement is structural: AuthenticatedWrite is the only way for a mutating handler to reach a session, and constructing it runs the check. Same reasoning as hoisting the media-type/crit/url/nonce checks into AcmeRequest — a new endpoint cannot forget what it cannot express.

Structs

AdminClientIp

The peer address of an admin request, if the socket carried one.

Authenticated

A live session and the operator it belongs to. Read-only handlers take this.

AuthenticatedWrite

Authenticated, plus the CSRF token and the origin gate.

EnrolWrite

A session allowed to set up a factor.

LoginLimiter

Fixed-window failed-login counter, keyed by client address.

MintedToken

A freshly minted session token, and the hash to store for it.

PendingMfa

A session with a verified password and nothing more.

PendingMfaSubmit

PendingMfa with the origin gate only, and no CSRF check.

Enums

MfaStep

What still stands between a pending_mfa cookie and a usable session.

Constants

COOKIE_NAME

The session cookie’s name.

CSRF_HEADER

The header carrying the per-session CSRF token on unsafe methods.

PENDING_MFA_TTL

How long a half-authenticated session may sit unfinished.

Functions

check_csrf

Compares the request’s X-CSRF-Token against the session’s, in constant time.

check_origin

Refuses a request whose Origin or Sec-Fetch-Site says it came from somewhere else.

clearing_cookie

The Set-Cookie value that clears one.

cookie_value

Reads the session token out of a Cookie header set.

hash_token

hex(SHA-256(token)) — the admin_sessions primary key.

log_login

Logs a completed login attempt. One place, so the events cannot drift.

mint_csrf_token

Mints a CSRF token. Same entropy as a session token — it is stored in plaintext, but it still has to be unguessable.

mint_token

Mints a session token. RNG failure is unrecoverable, as elsewhere in this crate.

session_cookie

The Set-Cookie value that establishes a session.