techne-sdk 0.3.3

//! atproto inter-service-auth JWTs (ES256K): verify, pre-check, mint.
//!
//! Ported from regenOS `regenos_appview::auth::service_jwt` (P20.7 G4); the platform-only pieces
//! (`principal_for_jwt` and its Postgres upserts) stay there. [`crate::service_auth::ServiceAuth`]
//! composes these with a DID resolver and a `jti` cache.
//!
//! Cross-service calls carry a short-lived JWT minted by `com.atproto.server.getServiceAuth`, signed
//! by the account's `#atproto` signing key, with claims `iss` (account DID), `aud` (recipient service
//! DID), `lxm` (the lexicon method this token authorizes), `exp`, optional `iat`, and `jti`/`nonce`.
//!
//! - `iat` is OPTIONAL; `lxm` is REQUIRED; `jti` OR `nonce` is required (surfaced for the replay cache).
//! - `aud` accepts the bare service DID or that DID with the `#atproto_appview` fragment, nothing else.
//! - low-S is required (atproto malleability guard).
//! - a MAX lifetime ceiling ([`MAX_SERVICE_JWT_LIFETIME_SECS`]) bounds the fail-open `jti` cache's
//!   replay window.
//!
//! [`multibase_to_verifying_key`] decodes a `z…` secp256k1 multikey (rejecting P-256) into a key.

use base64::Engine;
use k256::ecdsa::signature::Verifier;
use k256::ecdsa::{Signature, VerifyingKey};

const B64: base64::engine::general_purpose::GeneralPurpose = base64::engine::general_purpose::URL_SAFE_NO_PAD;

/// The atproto multicodec prefix for a secp256k1 public key (`0xe7` varint-encoded as `0xe7 0x01`). The
/// `did:key` / DID-doc `#atproto` multibase encodes `prefix || compressed-sec1-pubkey`.
const MULTICODEC_SECP256K1: [u8; 2] = [0xe7, 0x01];
/// The multicodec prefix for a p256 (secp256r1) public key — REJECTED (we verify ES256K only).
const MULTICODEC_P256: [u8; 2] = [0x80, 0x24];

/// The maximum accepted lifetime (`exp - now`) of a Lane-B service-auth JWT. atproto `getServiceAuth`
/// tokens are short-lived (~60s); we reject anything claiming materially more. This makes REAL the §3.4
/// safety argument that the fail-OPEN `jti` replay cache's exposure is bounded by a short `exp`: without a
/// ceiling a signer could mint a years-long token that, during a cache outage, is replayable for its full
/// life. 300s is a generous bound over the ~60s convention (clock skew + minting latency).
pub const MAX_SERVICE_JWT_LIFETIME_SECS: u64 = 300;

/// Why a service-auth JWT was rejected. Every non-happy path is fail-closed to one of these.
#[derive(Debug, PartialEq, Eq)]
pub enum ServiceJwtError {
    /// Not three base64url segments / undecodable / non-JSON.
    Malformed,
    /// Header `alg` is not `ES256K` (we only accept the secp256k1 method).
    BadAlg,
    /// A required claim (`iss`/`aud`/`lxm`/`exp`, or a `jti`/`nonce`) is missing or the wrong type.
    MissingClaim,
    /// ECDSA verification against the resolved `#atproto` key failed (tamper / wrong signer).
    BadSignature,
    /// Signature was high-S — atproto requires low-S (malleability guard).
    HighS,
    /// `aud` is not this AppView's service DID — token minted for some other service.
    AudMismatch,
    /// `lxm` is not the method being called — token authorizes a different endpoint.
    LxmMismatch,
    /// `exp` is in the past.
    Expired,
    /// `exp` is too far in the future — the token's claimed lifetime exceeds
    /// [`MAX_SERVICE_JWT_LIFETIME_SECS`]. Bounds the fail-OPEN `jti` cache's replay window (§3.4).
    ExcessiveLifetime,
    /// The multibase `#atproto` key was undecodable, the wrong multicodec (e.g. p256), or not a valid
    /// secp256k1 point. Surfaced by [`multibase_to_verifying_key`].
    BadKey,
}

/// The claims we trust *after* signature + audience + method + expiry all pass.
#[derive(Debug, PartialEq, Eq)]
pub struct VerifiedClaims {
    /// `iss` — the account DID the request is on behalf of. Becomes `Principal::User(iss)`.
    pub iss: String,
    /// `lxm` — the method this token authorizes (== the called NSID). The Lane-B scope set is `[lxm]`.
    pub lxm: String,
    /// The replay nonce — `jti` if present, else `nonce`. The caller feeds this to the `JtiCache`.
    pub jti: String,
    /// `exp` (unix seconds) — surfaced so the caller can record `(jti, exp)` in the replay cache.
    pub exp: u64,
}

/// Sign `msg` with the k256 private key given as hex (`hex_priv`), returning the base64url-nopad
/// (`r‖s`, 64 bytes) signature. k256's `Signer` always produces a LOW-S signature. `None` on
/// malformed hex / an invalid scalar (bad key material is a caller config error, never a panic).
/// [`multibase_to_verifying_key`] over the published `#atproto` key is its verification inverse.
pub fn sign_bytes(hex_priv: &str, msg: &[u8]) -> Option<String> {
    use k256::ecdsa::signature::Signer;
    use k256::ecdsa::{Signature, SigningKey};

    let priv_bytes = hex::decode(hex_priv.trim()).ok()?;
    let sk = SigningKey::from_slice(&priv_bytes).ok()?;
    let sig: Signature = sk.sign(msg);
    Some(B64.encode(sig.to_bytes()))
}

/// Mint an atproto inter-service-auth JWT (ES256K) signed with the caller's own service key: the
/// outbound twin of [`verify_service_jwt`]. `iss` is the caller's service DID (whose DID document
/// publishes the key at `#atproto`), `aud` the callee's DID, `lxm` the one method it authorizes;
/// `exp` is `now_unix + ttl_secs`, and a fresh random `jti` makes each token single-use. `None` on
/// malformed key material.
pub fn mint_service_jwt(hex_priv: &str, iss: &str, aud: &str, lxm: &str, ttl_secs: u64, now_unix: u64) -> Option<String> {
    let mut nonce = [0u8; 16];
    getrandom::getrandom(&mut nonce).ok()?;
    let header = serde_json::json!({ "typ": "JWT", "alg": "ES256K" });
    let payload = serde_json::json!({
        "iss": iss, "aud": aud, "lxm": lxm,
        "iat": now_unix, "exp": now_unix + ttl_secs, "jti": hex::encode(nonce),
    });
    let signing_input = format!(
        "{}.{}",
        B64.encode(serde_json::to_vec(&header).ok()?),
        B64.encode(serde_json::to_vec(&payload).ok()?)
    );
    let sig = sign_bytes(hex_priv, signing_input.as_bytes())?;
    Some(format!("{signing_input}.{sig}"))
}

/// Verify an atproto inter-service-auth JWT, GIVEN the signer's already-resolved `#atproto` key.
///
/// Ordering is fail-closed: structure → alg → signature → low-S → aud → lxm → expiry → required claims.
/// The signature is checked BEFORE any claim is trusted. `now_unix` is injected so the check is
/// deterministic in tests. Replay (`jti`) dedup is the CALLER's responsibility (it has the cache); this
/// function only surfaces the nonce in [`VerifiedClaims::jti`].
pub fn verify_service_jwt(
    token: &str,
    signer_key: &VerifyingKey,
    expected_aud: &str,
    expected_lxm: &str,
    now_unix: u64,
) -> Result<VerifiedClaims, ServiceJwtError> {
    // 1. Split `header.payload.signature`.
    let parts: Vec<&str> = token.split('.').collect();
    if parts.len() != 3 {
        return Err(ServiceJwtError::Malformed);
    }
    let (b64_header, b64_payload, b64_sig) = (parts[0], parts[1], parts[2]);

    // 2. Header: must be ES256K (the secp256k1 JWS alg).
    let header: serde_json::Value = decode_json(b64_header)?;
    if header.get("alg").and_then(|v| v.as_str()) != Some("ES256K") {
        return Err(ServiceJwtError::BadAlg);
    }

    // 3. Signature, over the ASCII `header.payload` signing input. k256 hashes SHA-256 internally,
    //    matching JWS ES256K. We verify the signature BEFORE trusting any claim.
    let sig_bytes = B64.decode(b64_sig).map_err(|_| ServiceJwtError::Malformed)?;
    let sig = Signature::from_slice(&sig_bytes).map_err(|_| ServiceJwtError::Malformed)?;
    if sig.normalize_s().is_some() {
        // `normalize_s` returns Some only when the input was high-S — atproto requires low-S.
        return Err(ServiceJwtError::HighS);
    }
    let signing_input = format!("{b64_header}.{b64_payload}");
    signer_key
        .verify(signing_input.as_bytes(), &sig)
        .map_err(|_| ServiceJwtError::BadSignature)?;

    // 4. Claims — only now that the signature holds.
    let payload: serde_json::Value = decode_json(b64_payload)?;
    let iss = claim_str(&payload, "iss")?;
    let aud = claim_str(&payload, "aud")?;
    let lxm = claim_str(&payload, "lxm")?;
    let exp = claim_u64(&payload, "exp")?;
    // §3.4: `iat` is OPTIONAL — read it if present, never error on its absence.
    let _iat = payload.get("iat").and_then(|v| v.as_u64());
    // §3.4: accept `jti` OR `nonce` (a PDS emits `jti`; a lex-server reads `nonce`). At least one is
    // required so the replay cache has a key.
    let jti = payload
        .get("jti")
        .and_then(|v| v.as_str())
        .or_else(|| payload.get("nonce").and_then(|v| v.as_str()))
        .map(str::to_owned)
        .ok_or(ServiceJwtError::MissingClaim)?;

    // §3.4: `aud` accepts BOTH the bare service DID and the `#atproto_appview` fragment form (forward-safe).
    if !aud_matches(&aud, expected_aud) {
        return Err(ServiceJwtError::AudMismatch);
    }
    if !lxm_matches(&lxm, expected_lxm, now_unix) {
        return Err(ServiceJwtError::LxmMismatch);
    }
    if now_unix >= exp {
        return Err(ServiceJwtError::Expired);
    }
    // Lifetime ceiling: `exp > now` here (checked above), so `exp - now` is the remaining life. A token
    // claiming materially more than the ~60s service-auth convention is rejected, keeping the fail-OPEN
    // `jti` cache's replay window bounded (§3.4).
    if exp - now_unix > MAX_SERVICE_JWT_LIFETIME_SECS {
        return Err(ServiceJwtError::ExcessiveLifetime);
    }

    Ok(VerifiedClaims { iss, lxm, jti, exp })
}

/// The one service fragment an `aud` may carry.
const AUD_FRAGMENT: &str = "#atproto_appview";

/// `aud` matches iff it is the expected service DID, bare or with the `#atproto_appview` fragment.
/// The configured DID may carry that fragment too. Any other fragment (`#bsky_appview`,
/// `#atproto_labeler`, ...) names a different service and is refused, as is a configured DID with one.
fn aud_matches(aud: &str, expected: &str) -> bool {
    let bare = |s: &str| -> Option<String> {
        let did = s.strip_suffix(AUD_FRAGMENT).unwrap_or(s);
        (!did.is_empty() && !did.contains('#')).then(|| did.to_owned())
    };
    matches!((bare(aud), bare(expected)), (Some(a), Some(e)) if a == e)
}

/// The decode inverse of the `did:key` multikey encoder ([`crate::labels::multibase`]): a multibase
/// (`z`-prefixed base58btc) secp256k1 public key → a [`VerifyingKey`].
///
/// Steps: strip the leading `z` → `bs58::decode` → assert the multicodec prefix is `[0xe7,0x01]` (REJECT
/// p256 `[0x80,0x24]` and anything else) → `VerifyingKey::from_sec1_bytes(&bytes[2..])` over the
/// remaining compressed SEC1 point. Any failure → [`ServiceJwtError::BadKey`].
pub fn multibase_to_verifying_key(s: &str) -> Result<VerifyingKey, ServiceJwtError> {
    // Multibase base58btc is `z`-prefixed (the only base atproto did:key uses).
    let b58 = s.strip_prefix('z').ok_or(ServiceJwtError::BadKey)?;
    let bytes = bs58::decode(b58).into_vec().map_err(|_| ServiceJwtError::BadKey)?;
    if bytes.len() < 2 {
        return Err(ServiceJwtError::BadKey);
    }
    let prefix = [bytes[0], bytes[1]];
    if prefix == MULTICODEC_P256 {
        // Explicitly reject p256 — we verify ES256K only.
        return Err(ServiceJwtError::BadKey);
    }
    if prefix != MULTICODEC_SECP256K1 {
        return Err(ServiceJwtError::BadKey);
    }
    VerifyingKey::from_sec1_bytes(&bytes[2..]).map_err(|_| ServiceJwtError::BadKey)
}

/// `lxm` binds the called method `expected`: the same name, or an old name of it that the platform's
/// rename map still honours on `now_unix`'s day (C6.3, N1, as the platform's `lxm_matches`: the alias
/// layer renames an old method path before auth, while a draft-era client's token still names the method
/// it called). Never the other way round.
fn lxm_matches(lxm: &str, expected: &str, now_unix: u64) -> bool {
    lxm == expected || crate::renames::current_name_at(lxm, now_unix) == Some(expected)
}

/// The cheap, crypto-free, I/O-free Lane-B claims pre-check (§3.4 DoS bound). Decode the UNVERIFIED JWT
/// payload (the middle base64url-no-pad segment) ONCE and reject early on the four pure-local conditions —
/// in the cheapest-first order — returning the `iss` string ONLY for a token that survives all of them:
///   1. `aud == our service DID` (the strongest, cheapest filter: a pure string compare, no crypto, no I/O —
///      a flood of Bearers minted for some OTHER service is dropped here, before any PLC lookup);
///   2. `lxm` is present AND binds the called `nsid` ([`lxm_matches`]: the same name, or an old name of it);
///   3. `exp` is present AND `> now` (not expired);
///   4. `iss` is present AND a SYNTACTIC DID ([`crate::did::is_did`] — a pure local validation).
///
/// Returns `None` (⇒ no resolution, held to Anonymous) on ANY structural/decoding failure or any of the
/// four rejections. This reads the UNVERIFIED payload, so it is a fast REJECT-ONLY filter: the
/// signature/crypto in [`verify_service_jwt`] RE-checks every one of these against the signed payload before
/// any authority is granted, so a forged claim that slips the pre-check is still caught post-resolution.
///
/// Public so every service that verifies these tokens ([`crate::service_auth::ServiceAuth`]) runs the
/// identical pre-check → resolve → verify → replay pipeline.
pub fn precheck_claims(jwt: &str, expected_aud: &str, expected_lxm: &str, now_unix: u64) -> Option<String> {
    let payload_b64 = jwt.split('.').nth(1)?;
    let bytes = B64.decode(payload_b64).ok()?;
    let payload: serde_json::Value = serde_json::from_slice(&bytes).ok()?;

    // 1. `aud` — the cheapest, strongest filter (pure string compare). A token for another service stops here.
    let aud = payload.get("aud").and_then(|v| v.as_str())?;
    if !aud_matches(aud, expected_aud) {
        return None;
    }
    // 2. `lxm` — must be present and bind to the called method.
    let lxm = payload.get("lxm").and_then(|v| v.as_str())?;
    if !lxm_matches(lxm, expected_lxm, now_unix) {
        return None;
    }
    // 3. `exp` — must be present and in the future.
    let exp = payload.get("exp").and_then(|v| v.as_u64())?;
    if now_unix >= exp {
        return None;
    }
    // 3b. Lifetime ceiling (§3.4 — DoS + fail-open-cache bound): reject a token claiming a lifetime far
    // beyond the ~60s service-auth convention BEFORE resolving its DID. `verify_service_jwt` re-checks this.
    if exp - now_unix > MAX_SERVICE_JWT_LIFETIME_SECS {
        return None;
    }
    // 4. `iss` — must be present and a syntactic DID (so we never resolve a non-DID string).
    let iss = payload.get("iss").and_then(|v| v.as_str())?;
    if !crate::did::is_did(iss) {
        return None;
    }
    Some(iss.to_owned())
}

fn decode_json(seg: &str) -> Result<serde_json::Value, ServiceJwtError> {
    let bytes = B64.decode(seg).map_err(|_| ServiceJwtError::Malformed)?;
    serde_json::from_slice(&bytes).map_err(|_| ServiceJwtError::Malformed)
}

fn claim_str(payload: &serde_json::Value, key: &str) -> Result<String, ServiceJwtError> {
    payload
        .get(key)
        .and_then(|v| v.as_str())
        .map(str::to_owned)
        .ok_or(ServiceJwtError::MissingClaim)
}

fn claim_u64(payload: &serde_json::Value, key: &str) -> Result<u64, ServiceJwtError> {
    payload
        .get(key)
        .and_then(|v| v.as_u64())
        .ok_or(ServiceJwtError::MissingClaim)
}

#[cfg(test)]
mod tests {
    use super::*;
    use k256::ecdsa::signature::Signer;
    use k256::ecdsa::SigningKey;

    const ISS: &str = "did:plc:alice0000000000000000000";
    const AUD: &str = "did:web:scenius.makewith.you"; // the AppView service DID
    const LXM: &str = "pub.techne.draft.getMyAttention";
    const NOW: u64 = 1_750_000_000;

    fn keypair() -> (SigningKey, VerifyingKey) {
        // Deterministic secp256k1 test scalar (mirrors identity::keys::FileEnvKeyStore::for_test).
        let sk = SigningKey::from_slice(&[0x11u8; 32]).expect("valid scalar");
        let vk = *sk.verifying_key();
        (sk, vk)
    }

    /// Test-only minter: stands in for `com.atproto.server.getServiceAuth` so the round-trip is
    /// self-contained. `iat`/`jti`/`nonce` are passed through so the gap-fix tests can vary them.
    /// Borrowed params for the test-only [`mint`] minter (the arg list was 8).
    struct MintParams<'a> {
        signing_key: &'a SigningKey,
        iss: &'a str,
        aud: &'a str,
        lxm: &'a str,
        exp: u64,
        iat: Option<u64>,
        jti: Option<&'a str>,
        nonce: Option<&'a str>,
    }

    fn mint(p: MintParams<'_>) -> String {
        let MintParams { signing_key, iss, aud, lxm, exp, iat, jti, nonce } = p;
        let header = serde_json::json!({ "typ": "JWT", "alg": "ES256K" });
        let mut payload = serde_json::json!({ "iss": iss, "aud": aud, "lxm": lxm, "exp": exp });
        if let Some(iat) = iat {
            payload["iat"] = serde_json::json!(iat);
        }
        if let Some(jti) = jti {
            payload["jti"] = serde_json::json!(jti);
        }
        if let Some(nonce) = nonce {
            payload["nonce"] = serde_json::json!(nonce);
        }
        let b64_header = B64.encode(serde_json::to_vec(&header).unwrap());
        let b64_payload = B64.encode(serde_json::to_vec(&payload).unwrap());
        let signing_input = format!("{b64_header}.{b64_payload}");
        let sig: Signature = signing_key.sign(signing_input.as_bytes());
        let b64_sig = B64.encode(sig.to_bytes());
        format!("{signing_input}.{b64_sig}")
    }

    fn good_token(sk: &SigningKey) -> String {
        mint(MintParams { signing_key: sk, iss: ISS, aud: AUD, lxm: LXM, exp: NOW + 60, iat: Some(NOW), jti: Some("nonce-0001"), nonce: None })
    }

    // ── the 8 promoted spike tests ──────────────────────────────────────────────────────────────

    #[test]
    fn valid_token_verifies_and_yields_the_issuer_did() {
        let (sk, vk) = keypair();
        let claims = verify_service_jwt(&good_token(&sk), &vk, AUD, LXM, NOW).expect("should verify");
        assert_eq!(claims.iss, ISS, "iss becomes Principal::User(iss)");
        assert_eq!(claims.lxm, LXM);
        assert_eq!(claims.jti, "nonce-0001");
        assert_eq!(claims.exp, NOW + 60);
    }

    #[test]
    fn tampered_payload_fails_signature() {
        let (sk, vk) = keypair();
        let token = good_token(&sk);
        let mut parts: Vec<String> = token.split('.').map(str::to_owned).collect();
        let forged = serde_json::json!({
            "iss": "did:plc:mallory00000000000000000", "aud": AUD, "lxm": LXM, "exp": NOW + 60, "iat": NOW, "jti": "x",
        });
        parts[1] = B64.encode(serde_json::to_vec(&forged).unwrap());
        let token = parts.join(".");
        assert_eq!(verify_service_jwt(&token, &vk, AUD, LXM, NOW), Err(ServiceJwtError::BadSignature));
    }

    #[test]
    fn wrong_signer_key_fails_signature() {
        let (sk, _) = keypair();
        let other = SigningKey::from_slice(&[0x22u8; 32]).unwrap();
        let wrong_vk = *other.verifying_key();
        assert_eq!(
            verify_service_jwt(&good_token(&sk), &wrong_vk, AUD, LXM, NOW),
            Err(ServiceJwtError::BadSignature)
        );
    }

    #[test]
    fn token_for_another_service_is_rejected() {
        let (sk, vk) = keypair();
        let token = mint(MintParams { signing_key: &sk, iss: ISS, aud: "did:web:someone-else.example", lxm: LXM, exp: NOW + 60, iat: Some(NOW), jti: Some("x"), nonce: None });
        assert_eq!(verify_service_jwt(&token, &vk, AUD, LXM, NOW), Err(ServiceJwtError::AudMismatch));
    }

    #[test]
    fn token_for_another_method_is_rejected() {
        let (sk, vk) = keypair();
        let token = mint(MintParams { signing_key: &sk, iss: ISS, aud: AUD, lxm: "pub.techne.draft.deleteEverything", exp: NOW + 60, iat: Some(NOW), jti: Some("x"), nonce: None });
        assert_eq!(verify_service_jwt(&token, &vk, AUD, LXM, NOW), Err(ServiceJwtError::LxmMismatch));
    }

    #[test]
    fn expired_token_is_rejected() {
        let (sk, vk) = keypair();
        let token = mint(MintParams { signing_key: &sk, iss: ISS, aud: AUD, lxm: LXM, exp: NOW - 1, iat: Some(NOW - 61), jti: Some("x"), nonce: None });
        assert_eq!(verify_service_jwt(&token, &vk, AUD, LXM, NOW), Err(ServiceJwtError::Expired));
    }

    #[test]
    fn excessive_lifetime_is_rejected() {
        // A token whose exp is far beyond the ~60s service-auth convention is rejected, so the fail-OPEN
        // jti cache's replay window stays bounded (§3.4). A signer controls its own exp, so the ceiling
        // must be enforced by the VERIFIER, not assumed.
        let (sk, vk) = keypair();
        let token = mint(MintParams { signing_key: &sk, iss: ISS, aud: AUD, lxm: LXM, exp: NOW + 86_400, iat: Some(NOW), jti: Some("x"), nonce: None });
        assert_eq!(
            verify_service_jwt(&token, &vk, AUD, LXM, NOW),
            Err(ServiceJwtError::ExcessiveLifetime)
        );
        // Boundary is inclusive: exactly at the ceiling still verifies.
        let at_ceiling = mint(MintParams { signing_key: &sk, iss: ISS, aud: AUD, lxm: LXM, exp: NOW + MAX_SERVICE_JWT_LIFETIME_SECS, iat: Some(NOW), jti: Some("x"), nonce: None });
        assert!(verify_service_jwt(&at_ceiling, &vk, AUD, LXM, NOW).is_ok());
    }

    #[test]
    fn non_es256k_alg_is_rejected() {
        let (_, vk) = keypair();
        let header = B64.encode(br#"{"typ":"JWT","alg":"HS256"}"#);
        let payload = B64.encode(br#"{"iss":"x","aud":"x","lxm":"x","exp":9999999999,"iat":1,"jti":"x"}"#);
        let token = format!("{header}.{payload}.{}", B64.encode([0u8; 64]));
        assert_eq!(verify_service_jwt(&token, &vk, AUD, LXM, NOW), Err(ServiceJwtError::BadAlg));
    }

    #[test]
    fn garbage_is_rejected_not_panicked() {
        let (_, vk) = keypair();
        for junk in ["", "a.b", "...", "not-a-jwt", "a.b.c.d"] {
            assert!(verify_service_jwt(junk, &vk, AUD, LXM, NOW).is_err(), "junk {junk:?} must fail closed");
        }
    }

    // ── §3.4 verify-gap tests ───────────────────────────────────────────────────────────────────

    #[test]
    fn iat_is_optional() {
        // No `iat` at all — must still verify (the spike used to require it).
        let (sk, vk) = keypair();
        let token = mint(MintParams { signing_key: &sk, iss: ISS, aud: AUD, lxm: LXM, exp: NOW + 60, iat: None, jti: Some("x"), nonce: None });
        assert!(verify_service_jwt(&token, &vk, AUD, LXM, NOW).is_ok(), "iat must be optional");
    }

    #[test]
    fn lxm_is_required() {
        let (sk, vk) = keypair();
        // Mint without `lxm` — verify must reject as a missing claim.
        let header = B64.encode(br#"{"typ":"JWT","alg":"ES256K"}"#);
        let payload = serde_json::json!({ "iss": ISS, "aud": AUD, "exp": NOW + 60, "jti": "x" });
        let b64_payload = B64.encode(serde_json::to_vec(&payload).unwrap());
        let signing_input = format!("{header}.{b64_payload}");
        let sig: Signature = sk.sign(signing_input.as_bytes());
        let token = format!("{signing_input}.{}", B64.encode(sig.to_bytes()));
        assert_eq!(verify_service_jwt(&token, &vk, AUD, LXM, NOW), Err(ServiceJwtError::MissingClaim));
    }

    #[test]
    fn nonce_is_accepted_when_jti_absent() {
        let (sk, vk) = keypair();
        let token = mint(MintParams { signing_key: &sk, iss: ISS, aud: AUD, lxm: LXM, exp: NOW + 60, iat: Some(NOW), jti: None, nonce: Some("nonce-from-lexserver") });
        let claims = verify_service_jwt(&token, &vk, AUD, LXM, NOW).expect("nonce should be accepted");
        assert_eq!(claims.jti, "nonce-from-lexserver");
    }

    #[test]
    fn missing_jti_and_nonce_is_rejected() {
        let (sk, vk) = keypair();
        let token = mint(MintParams { signing_key: &sk, iss: ISS, aud: AUD, lxm: LXM, exp: NOW + 60, iat: Some(NOW), jti: None, nonce: None });
        assert_eq!(verify_service_jwt(&token, &vk, AUD, LXM, NOW), Err(ServiceJwtError::MissingClaim));
    }

    #[test]
    fn aud_accepts_the_atproto_appview_fragment_form() {
        let (sk, vk) = keypair();
        // Token carries the fragment; our configured aud is bare — must still match.
        let token = mint(MintParams { signing_key: &sk, iss: ISS, aud: &format!("{AUD}#atproto_appview"), lxm: LXM, exp: NOW + 60, iat: Some(NOW), jti: Some("x"), nonce: None });
        assert!(verify_service_jwt(&token, &vk, AUD, LXM, NOW).is_ok());
        // And the symmetric case: configured aud carries the fragment, token is bare.
        let token2 = good_token(&sk);
        assert!(verify_service_jwt(&token2, &vk, &format!("{AUD}#atproto_appview"), LXM, NOW).is_ok());
    }

    #[test]
    fn aud_refuses_any_other_fragment() {
        let (sk, vk) = keypair();
        for aud in [format!("{AUD}#bsky_appview"), format!("{AUD}#atproto_labeler"), format!("{AUD}#"), format!("{AUD}#atproto_appview#atproto_appview")] {
            let token = mint(MintParams { signing_key: &sk, iss: ISS, aud: &aud, lxm: LXM, exp: NOW + 60, iat: Some(NOW), jti: Some("x"), nonce: None });
            assert_eq!(verify_service_jwt(&token, &vk, AUD, LXM, NOW).err(), Some(ServiceJwtError::AudMismatch), "{aud}");
            assert_eq!(precheck_claims(&token, AUD, LXM, NOW), None, "{aud}");
        }
        // A configured DID with another fragment matches nothing, not even itself.
        let token = mint(MintParams { signing_key: &sk, iss: ISS, aud: &format!("{AUD}#other"), lxm: LXM, exp: NOW + 60, iat: Some(NOW), jti: Some("x"), nonce: None });
        assert_eq!(verify_service_jwt(&token, &vk, &format!("{AUD}#other"), LXM, NOW).err(), Some(ServiceJwtError::AudMismatch));
        assert!(!aud_matches(AUD, &format!("{AUD}#other")));
        assert!(!aud_matches("#atproto_appview", "#atproto_appview"));
    }

    #[test]
    fn high_s_signature_is_rejected() {
        // Construct a high-S signature by negating S of a valid low-S signature. atproto requires low-S.
        let (sk, vk) = keypair();
        let header = B64.encode(br#"{"typ":"JWT","alg":"ES256K"}"#);
        let payload = serde_json::json!({ "iss": ISS, "aud": AUD, "lxm": LXM, "exp": NOW + 60, "jti": "x" });
        let b64_payload = B64.encode(serde_json::to_vec(&payload).unwrap());
        let signing_input = format!("{header}.{b64_payload}");
        let sig: Signature = sk.sign(signing_input.as_bytes());
        // k256 always produces low-S; flip to high-S so the verifier's low-S guard fires.
        let high = sig.normalize_s().unwrap_or(sig);
        // `normalize_s` returns the low-S form; to get a high-S we need the complement. Compute it.
        let high_s_sig = {
            // S' = n - S yields the high-S counterpart. Use the scalar arithmetic via the signature bytes.
            use k256::elliptic_curve::scalar::IsHigh;
            let s = high.s();
            let neg_s = -*s;
            // If S was already low, -S is high.
            let candidate = Signature::from_scalars(*high.r(), neg_s).unwrap();
            assert!(bool::from(candidate.s().is_high()), "candidate must be high-S");
            candidate
        };
        let token = format!("{signing_input}.{}", B64.encode(high_s_sig.to_bytes()));
        assert_eq!(verify_service_jwt(&token, &vk, AUD, LXM, NOW), Err(ServiceJwtError::HighS));
    }

    // ── multibase_to_verifying_key: the decode inverse of keys.rs ───────────────────────────────

    /// Encode a VerifyingKey the way `keys.rs:121-131` does, so the decode round-trips.
    fn encode_did_key_multibase(vk: &VerifyingKey) -> String {
        let compressed = vk.to_encoded_point(true);
        let mut prefixed = Vec::with_capacity(2 + compressed.as_bytes().len());
        prefixed.extend_from_slice(&MULTICODEC_SECP256K1);
        prefixed.extend_from_slice(compressed.as_bytes());
        format!("z{}", bs58::encode(prefixed).into_string())
    }

    #[test]
    fn multibase_round_trips_the_keys_rs_encoder() {
        let (_, vk) = keypair();
        let mb = encode_did_key_multibase(&vk);
        let decoded = multibase_to_verifying_key(&mb).expect("should decode our own encoding");
        assert_eq!(decoded, vk, "decode must invert the keys.rs encoder");
    }

    #[test]
    fn multibase_rejects_p256_multicodec() {
        // A `z`-prefixed base58 of the p256 multicodec + 33 junk bytes — must be rejected (BadKey),
        // never silently treated as secp256k1.
        let mut bytes = MULTICODEC_P256.to_vec();
        bytes.extend_from_slice(&[0x02; 33]);
        let mb = format!("z{}", bs58::encode(&bytes).into_string());
        assert_eq!(multibase_to_verifying_key(&mb), Err(ServiceJwtError::BadKey));
    }

    #[test]
    fn multibase_rejects_garbage() {
        assert_eq!(multibase_to_verifying_key(""), Err(ServiceJwtError::BadKey)); // no `z`
        assert_eq!(multibase_to_verifying_key("zzz!!!"), Err(ServiceJwtError::BadKey)); // bad base58
        assert_eq!(multibase_to_verifying_key("z"), Err(ServiceJwtError::BadKey)); // empty body
    }

    #[test]
    fn verify_chains_through_a_resolved_multibase_key() {
        // The end-to-end Lane-B shape: a DID-doc multibase string → key → verify a real token.
        let (sk, vk) = keypair();
        let mb = encode_did_key_multibase(&vk);
        let resolved = multibase_to_verifying_key(&mb).unwrap();
        let claims = verify_service_jwt(&good_token(&sk), &resolved, AUD, LXM, NOW).expect("verify");
        assert_eq!(claims.iss, ISS);
    }

    // ── sign_bytes: the channelVerification writer's signing primitive ────────────────────────────

    #[test]
    fn sign_bytes_round_trips_through_verifying_key() {
        use k256::ecdsa::signature::Verifier;

        let (sk, vk) = keypair();
        let hex_priv = hex::encode(sk.to_bytes());
        let msg = b"the quick brown fox";
        let sig_b64 = sign_bytes(&hex_priv, msg).expect("valid scalar signs");
        let sig_bytes = B64.decode(&sig_b64).expect("base64url-nopad");
        let sig = Signature::from_slice(&sig_bytes).expect("64-byte r||s");
        assert!(vk.verify(msg, &sig).is_ok(), "the resolved verifying key must accept the signature");
    }

    #[test]
    fn sign_bytes_is_deterministic_and_message_bound() {
        let (sk, _) = keypair();
        let hex_priv = hex::encode(sk.to_bytes());
        let a = sign_bytes(&hex_priv, b"payload a").unwrap();
        let b = sign_bytes(&hex_priv, b"payload a").unwrap();
        assert_eq!(a, b, "RFC 6979 deterministic ECDSA: same key + same message ⇒ same signature");
        let c = sign_bytes(&hex_priv, b"payload b").unwrap();
        assert_ne!(a, c, "a different message must yield a different signature");
    }

    #[test]
    fn sign_bytes_is_always_low_s() {
        let (sk, _) = keypair();
        let hex_priv = hex::encode(sk.to_bytes());
        for msg in [&b"one"[..], b"two", b"three-longer-message"] {
            let sig_b64 = sign_bytes(&hex_priv, msg).unwrap();
            let sig_bytes = B64.decode(&sig_b64).unwrap();
            let sig = Signature::from_slice(&sig_bytes).unwrap();
            assert!(sig.normalize_s().is_none(), "k256 must produce a low-S signature");
        }
    }

    #[test]
    fn sign_bytes_rejects_malformed_key_material() {
        assert!(sign_bytes("not-hex", b"msg").is_none());
        assert!(sign_bytes("00", b"msg").is_none(), "wrong-length scalar");
    }

    /// The last day the platform's rename map honours `old` (its `closeEarlier` date, else `deleteAfter`),
    /// as a unix time at noon UTC that day; read straight off the crate's copy of the map.
    fn last_day_noon(old: &str) -> u64 {
        let doc: serde_json::Value = serde_json::from_str(include_str!("nsid_renames.json")).unwrap();
        let early = doc["closeEarlier"].as_object().unwrap().iter().find(|(_, olds)| olds.as_array().unwrap().iter().any(|o| o == old));
        let day = early.map(|(d, _)| d.as_str()).unwrap_or_else(|| doc["deleteAfter"].as_str().unwrap());
        let date = chrono::NaiveDate::parse_from_str(day, "%Y-%m-%d").unwrap();
        date.and_hms_opt(12, 0, 0).unwrap().and_utc().timestamp() as u64
    }

    /// C6.3 (N1, the platform's 2ebc41bf6): a token minted for an old name of the called method (a
    /// draft-era client through the PDS proxy asks for `lxm` = the name it calls; the alias layer renamed
    /// the path before auth) binds the method while the rename map honours that name, and is refused from
    /// the day after its window closes. Never the other way round, nor another method. Both kinds of
    /// pair: a pre-N1 method rename (social.scenius.*Scene, closes early) and an N1 one (coop.lexicon.draft.*).
    #[test]
    fn an_old_name_of_the_called_method_binds_inside_its_window_only() {
        let (sk, vk) = keypair();
        let doc: serde_json::Value = serde_json::from_str(include_str!("nsid_renames.json")).unwrap();
        let renames = doc["renames"].as_object().unwrap();
        let pair = |pick: &dyn Fn(&str) -> bool| {
            let (o, n) = renames.iter().find(|(o, _)| pick(o)).expect("a renamed method");
            (o.clone(), n.as_str().unwrap().to_owned())
        };
        let pre_n1 = pair(&|o| o.starts_with("social.scenius."));
        let n1 = pair(&|o| o.ends_with(".commons.runChain"));
        for (old_m, new_m) in [pre_n1, n1] {
            let (old_m, new_m) = (old_m.as_str(), new_m.as_str());
            let token = mint(MintParams { signing_key: &sk, iss: ISS, aud: AUD, lxm: old_m, exp: NOW + 60, iat: Some(NOW), jti: Some("x"), nonce: None });
            let claims = verify_service_jwt(&token, &vk, AUD, new_m, NOW).unwrap_or_else(|e| panic!("{old_m} binds {new_m}: {e:?}"));
            assert_eq!(claims.lxm, old_m);
            assert_eq!(precheck_claims(&token, AUD, new_m, NOW).as_deref(), Some(ISS), "{old_m} prechecks for {new_m}");
            // The last day itself is inside the window; the day after is not.
            let last = last_day_noon(old_m);
            let on_last = mint(MintParams { signing_key: &sk, iss: ISS, aud: AUD, lxm: old_m, exp: last + 60, iat: Some(last), jti: Some("w"), nonce: None });
            assert!(verify_service_jwt(&on_last, &vk, AUD, new_m, last).is_ok(), "{old_m}: honoured through its last day");
            let after = last + 86_400;
            let late = mint(MintParams { signing_key: &sk, iss: ISS, aud: AUD, lxm: old_m, exp: after + 60, iat: Some(after), jti: Some("y"), nonce: None });
            assert_eq!(verify_service_jwt(&late, &vk, AUD, new_m, after), Err(ServiceJwtError::LxmMismatch), "{old_m} after its window");
            assert!(precheck_claims(&late, AUD, new_m, after).is_none());
            // Never the other way: a current-name token does not bind an old name, nor another method.
            let current = mint(MintParams { signing_key: &sk, iss: ISS, aud: AUD, lxm: new_m, exp: NOW + 60, iat: Some(NOW), jti: Some("z"), nonce: None });
            assert_eq!(verify_service_jwt(&current, &vk, AUD, old_m, NOW), Err(ServiceJwtError::LxmMismatch));
            assert!(precheck_claims(&current, AUD, old_m, NOW).is_none(), "{new_m} does not precheck for {old_m}");
            assert_eq!(verify_service_jwt(&token, &vk, AUD, LXM, NOW), Err(ServiceJwtError::LxmMismatch));
            assert!(precheck_claims(&token, AUD, LXM, NOW).is_none());
        }
    }
}

#[cfg(test)]
mod mint_tests {
    use super::*;

    /// The outbound token verifies under the key the signer publishes, for exactly its aud and lxm.
    #[test]
    fn a_minted_token_verifies_for_its_aud_and_lxm_only() {
        let hex_priv = hex::encode([0x22u8; 32]);
        let sk = k256::ecdsa::SigningKey::from_slice(&[0x22u8; 32]).unwrap();
        let vk = *sk.verifying_key();
        let lxm = "pub.techne.draft.commons.runChain";
        let now = 1_750_000_000;
        let jwt = mint_service_jwt(&hex_priv, "did:web:appview.example", "did:web:rules.example", lxm, 60, now).unwrap();
        let claims = verify_service_jwt(&jwt, &vk, "did:web:rules.example", lxm, now + 1).unwrap();
        assert_eq!(claims.iss, "did:web:appview.example");
        assert!(verify_service_jwt(&jwt, &vk, "did:web:other.example", lxm, now + 1).is_err());
        assert!(verify_service_jwt(&jwt, &vk, "did:web:rules.example", "pub.techne.draft.getEvent", now + 1).is_err());
        assert!(verify_service_jwt(&jwt, &vk, "did:web:rules.example", lxm, now + 120).is_err(), "expired");
        assert!(mint_service_jwt("not hex", "a", "b", lxm, 60, now).is_none());
    }

}