feat(admin): allowlist + integrity-MAC data model [operator §0.3/§1.2]

The admin authorization data model. The server stores only public keys; an admin
is authorized by presence in admin_keys, and each row carries an HMAC
(ADMIN_KEY_INTEGRITY_SECRET, separate from DATABASE_URL) over
id|pubkey|scope|created_at|activated_at|revoked_at. Because the MAC covers the
revocation/activation state, a DB-write attacker who clears revoked_at (un-revoke)
or revives a key produces a mismatch the guard rejects — the MAC proves a pubkey
is *currently* authorized, not merely once.

- migration 20260625000002: admin_keys (partial unique index = one active row per
  pubkey; soft revoke keeps history) + admin_sessions (separate table/secret from
  user sessions; cascade-on-key-delete).
- core::crypto::admin_mac: compute/verify over a JSON-canonical field set,
  timestamps as microsecond epochs; constant-time compare; KATs bind
  revoked/activated state.
- db::admin_keys: create / get_active (re-verifies MAC, fail-closed + logs tamper)
  / list / count_live / activate / revoke. Every covered-field write recomputes
  the MAC centrally; timestamps truncated to microseconds so the signed value
  round-trips; revoke/activate are FOR UPDATE transactions.
- 5 L1 tests incl. the load-bearing raw-SQL un-revoke -> MAC mismatch -> rejected.

src/core/crypto/admin_mac.rs

@@ -0,0 +1,104 @@
+//! Row-integrity MAC for the admin allowlist.
+//!
+//! Each `admin_keys` row carries an HMAC over its authorization-bearing fields,
+//! keyed by `ADMIN_KEY_INTEGRITY_SECRET` (deliberately separate from
+//! `DATABASE_URL`). Because the MAC covers `activated_at` AND `revoked_at`, a
+//! DB-write attacker who flips `revoked_at` back to `NULL` (un-revoke) or revives
+//! a key produces a mismatch the guard rejects — the MAC proves a pubkey is
+//! *currently* authorized, not merely that it once was. Every write that changes
+//! a covered field MUST recompute the MAC (the db layer does this centrally).
+
+use chrono::{DateTime, Utc};
+use subtle::ConstantTimeEq;
+use uuid::Uuid;
+
+use super::pepper::peppered_hex;
+
+/// The covered fields. Timestamps are compared at microsecond precision (the
+/// resolution Postgres stores), so the MAC round-trips exactly.
+pub struct AdminKeyMacInput<'a> {
+    pub id: Uuid,
+    pub pubkey: &'a str,
+    pub scope: &'a str,
+    pub created_at: DateTime<Utc>,
+    pub activated_at: Option<DateTime<Utc>>,
+    pub revoked_at: Option<DateTime<Utc>>,
+}
+
+/// `hex(HMAC-SHA256(secret, "admin_key_mac" ‖ canonical))`. The canonical form is
+/// a JSON array (unambiguous escaping) of the covered fields, timestamps as
+/// microsecond epochs (`null` when absent — so present-but-zero ≠ absent).
+pub fn compute_admin_key_mac(secret: &str, input: &AdminKeyMacInput) -> String {
+    let canonical = serde_json::json!([
+        input.id.to_string(),
+        input.pubkey,
+        input.scope,
+        input.created_at.timestamp_micros(),
+        input.activated_at.map(|t| t.timestamp_micros()),
+        input.revoked_at.map(|t| t.timestamp_micros()),
+    ])
+    .to_string();
+    peppered_hex(secret, "admin_key_mac", &canonical)
+}
+
+/// Constant-time check of a stored MAC against the recomputed one.
+pub fn verify_admin_key_mac(secret: &str, input: &AdminKeyMacInput, mac_hex: &str) -> bool {
+    let expected = compute_admin_key_mac(secret, input);
+    expected.as_bytes().ct_eq(mac_hex.as_bytes()).into()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const PK: &str = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
+
+    fn input() -> AdminKeyMacInput<'static> {
+        AdminKeyMacInput {
+            id: Uuid::from_u128(1),
+            pubkey: PK,
+            scope: "admin",
+            created_at: DateTime::from_timestamp(1_700_000_000, 0).unwrap(),
+            activated_at: None,
+            revoked_at: None,
+        }
+    }
+
+    #[test]
+    fn deterministic_and_verifies() {
+        let i = input();
+        let mac = compute_admin_key_mac("secret", &i);
+        assert!(verify_admin_key_mac("secret", &i, &mac));
+    }
+
+    #[test]
+    fn rejects_wrong_secret() {
+        let i = input();
+        let mac = compute_admin_key_mac("secret-A", &i);
+        assert!(!verify_admin_key_mac("secret-B", &i, &mac));
+    }
+
+    #[test]
+    fn revocation_state_is_bound() {
+        // The MAC for a revoked key must not validate once revoked_at is cleared
+        // (the un-revoke attack), and vice versa.
+        let active = input();
+        let mac_active = compute_admin_key_mac("secret", &active);
+
+        let mut revoked = input();
+        revoked.revoked_at = Some(DateTime::from_timestamp(1_700_000_500, 0).unwrap());
+        assert!(!verify_admin_key_mac("secret", &revoked, &mac_active));
+
+        let mac_revoked = compute_admin_key_mac("secret", &revoked);
+        assert!(!verify_admin_key_mac("secret", &active, &mac_revoked));
+    }
+
+    #[test]
+    fn activation_state_is_bound() {
+        let pending = input();
+        let mac_pending = compute_admin_key_mac("secret", &pending);
+        let mut activated = input();
+        activated.activated_at = Some(DateTime::from_timestamp(1_700_000_100, 0).unwrap());
+        assert!(!verify_admin_key_mac("secret", &activated, &mac_pending));
+    }
+}

src/core/crypto/mod.rs

@@ -1,5 +1,6 @@
 //! Cryptographic primitives: NIP-98 auth and wallet-signature verification.
 
+pub mod admin_mac;
 pub mod nip98;
 pub mod pepper;
 pub mod signatures;

src/infra/db/admin_keys.rs

@@ -0,0 +1,212 @@
+//! Admin allowlist queries.
+//!
+//! Every read of an active key re-verifies its integrity MAC, and every write
+//! that changes a covered field recomputes it, so MAC handling cannot drift or
+//! be forgotten by a caller. A MAC mismatch on read is treated as "not
+//! authorized" (fail-closed) and logged as tamper evidence. Timestamps bound by
+//! the MAC are truncated to microseconds (Postgres' resolution) so the value
+//! signed at write equals the value read back.
+
+use chrono::{SubsecRound, Utc};
+use tracing::instrument;
+use uuid::Uuid;
+
+use crate::core::crypto::admin_mac::{
+    compute_admin_key_mac, verify_admin_key_mac, AdminKeyMacInput,
+};
+use crate::error::AppError;
+use crate::models::db::{AdminKey, NewAdminKey};
+
+use super::{unique_violation_as, Database};
+
+/// Explicit `admin_keys` columns (FromRow maps by name).
+const COLS: &str = "id, pubkey, label, scope, created_at, created_by_kind, \
+     activated_at, activation_deadline, revoked_at, last_used_at, integrity_mac";
+
+fn mac_input<'a>(k: &'a AdminKey) -> AdminKeyMacInput<'a> {
+    AdminKeyMacInput {
+        id: k.id,
+        pubkey: &k.pubkey,
+        scope: &k.scope,
+        created_at: k.created_at,
+        activated_at: k.activated_at,
+        revoked_at: k.revoked_at,
+    }
+}
+
+impl Database {
+    /// Add an allowlist entry (pending — `activated_at` NULL until first login).
+    /// Fails 409 if an active key with this pubkey already exists.
+    #[instrument(skip(self, secret))]
+    pub async fn create_admin_key(
+        &self,
+        input: NewAdminKey,
+        secret: &str,
+    ) -> Result<AdminKey, AppError> {
+        let id = Uuid::new_v4();
+        let created_at = Utc::now().trunc_subsecs(6);
+        let mac = compute_admin_key_mac(
+            secret,
+            &AdminKeyMacInput {
+                id,
+                pubkey: &input.pubkey,
+                scope: &input.scope,
+                created_at,
+                activated_at: None,
+                revoked_at: None,
+            },
+        );
+        let sql = format!(
+            "INSERT INTO admin_keys \
+             (id, pubkey, label, scope, created_at, created_by_kind, activation_deadline, integrity_mac) \
+             VALUES ($1, $2, $3, $4, $5, $6, $7, $8) RETURNING {COLS}"
+        );
+        let key = sqlx::query_as::<_, AdminKey>(&sql)
+            .bind(id)
+            .bind(&input.pubkey)
+            .bind(&input.label)
+            .bind(&input.scope)
+            .bind(created_at)
+            .bind(&input.created_by_kind)
+            .bind(input.activation_deadline)
+            .bind(&mac)
+            .fetch_one(self.pool())
+            .await
+            .map_err(unique_violation_as(
+                "an active admin key with this pubkey already exists",
+            ))?;
+        Ok(key)
+    }
+
+    /// The active (non-revoked) allowlist entry for `pubkey`, IF its integrity
+    /// MAC verifies. A mismatch returns `None` (fail-closed) and logs tampering.
+    #[instrument(skip(self, secret))]
+    pub async fn get_active_admin_key(
+        &self,
+        pubkey: &str,
+        secret: &str,
+    ) -> Result<Option<AdminKey>, AppError> {
+        let sql = format!("SELECT {COLS} FROM admin_keys WHERE pubkey = $1 AND revoked_at IS NULL");
+        let row = sqlx::query_as::<_, AdminKey>(&sql)
+            .bind(pubkey)
+            .fetch_optional(self.pool())
+            .await?;
+        match row {
+            Some(key) if verify_admin_key_mac(secret, &mac_input(&key), &key.integrity_mac) => {
+                Ok(Some(key))
+            }
+            Some(key) => {
+                tracing::error!(
+                    admin_key_id = %key.id,
+                    "admin_keys integrity MAC mismatch — row tampered; rejecting"
+                );
+                Ok(None)
+            }
+            None => Ok(None),
+        }
+    }
+
+    /// All allowlist entries (active, pending, revoked), newest first.
+    #[instrument(skip(self))]
+    pub async fn list_admin_keys(&self) -> Result<Vec<AdminKey>, AppError> {
+        let sql = format!("SELECT {COLS} FROM admin_keys ORDER BY created_at DESC");
+        let rows = sqlx::query_as::<_, AdminKey>(&sql)
+            .fetch_all(self.pool())
+            .await?;
+        Ok(rows)
+    }
+
+    /// Count live (active + pending) keys — backs the `ADMIN_MAX_KEYS` cap.
+    #[instrument(skip(self))]
+    pub async fn count_live_admin_keys(&self) -> Result<i64, AppError> {
+        let n = sqlx::query_scalar::<_, i64>(
+            "SELECT COUNT(*) FROM admin_keys WHERE revoked_at IS NULL",
+        )
+        .fetch_one(self.pool())
+        .await?;
+        Ok(n)
+    }
+
+    /// Mark a pending key activated (first successful login). Recomputes the MAC.
+    /// Returns the updated row, or `None` if not pending (already active/revoked).
+    #[instrument(skip(self, secret))]
+    pub async fn activate_admin_key(
+        &self,
+        id: Uuid,
+        secret: &str,
+    ) -> Result<Option<AdminKey>, AppError> {
+        let mut tx = self.pool().begin().await?;
+        let sel = format!(
+            "SELECT {COLS} FROM admin_keys \
+             WHERE id = $1 AND revoked_at IS NULL AND activated_at IS NULL FOR UPDATE"
+        );
+        let Some(key) = sqlx::query_as::<_, AdminKey>(&sel)
+            .bind(id)
+            .fetch_optional(&mut *tx)
+            .await?
+        else {
+            tx.rollback().await?;
+            return Ok(None);
+        };
+        let activated_at = Utc::now().trunc_subsecs(6);
+        let mac = compute_admin_key_mac(
+            secret,
+            &AdminKeyMacInput {
+                activated_at: Some(activated_at),
+                ..mac_input(&key)
+            },
+        );
+        let upd = format!(
+            "UPDATE admin_keys SET activated_at = $2, integrity_mac = $3 WHERE id = $1 RETURNING {COLS}"
+        );
+        let updated = sqlx::query_as::<_, AdminKey>(&upd)
+            .bind(id)
+            .bind(activated_at)
+            .bind(&mac)
+            .fetch_one(&mut *tx)
+            .await?;
+        tx.commit().await?;
+        Ok(Some(updated))
+    }
+
+    /// Soft-revoke a key (recomputing the MAC over the new `revoked_at`). Returns
+    /// the updated row, or `None` if it was already revoked / does not exist.
+    #[instrument(skip(self, secret))]
+    pub async fn revoke_admin_key(
+        &self,
+        id: Uuid,
+        secret: &str,
+    ) -> Result<Option<AdminKey>, AppError> {
+        let mut tx = self.pool().begin().await?;
+        let sel = format!(
+            "SELECT {COLS} FROM admin_keys WHERE id = $1 AND revoked_at IS NULL FOR UPDATE"
+        );
+        let Some(key) = sqlx::query_as::<_, AdminKey>(&sel)
+            .bind(id)
+            .fetch_optional(&mut *tx)
+            .await?
+        else {
+            tx.rollback().await?;
+            return Ok(None);
+        };
+        let revoked_at = Utc::now().trunc_subsecs(6);
+        let mac = compute_admin_key_mac(
+            secret,
+            &AdminKeyMacInput {
+                revoked_at: Some(revoked_at),
+                ..mac_input(&key)
+            },
+        );
+        let upd = format!(
+            "UPDATE admin_keys SET revoked_at = $2, integrity_mac = $3 WHERE id = $1 RETURNING {COLS}"
+        );
+        let updated = sqlx::query_as::<_, AdminKey>(&upd)
+            .bind(id)
+            .bind(revoked_at)
+            .bind(&mac)
+            .fetch_one(&mut *tx)
+            .await?;
+        tx.commit().await?;
+        Ok(Some(updated))
+    }
+}

src/infra/db/mod.rs

@@ -6,6 +6,7 @@
 //! `seed_fingerprint`) are peppered inside these methods so the plaintext never
 //! reaches a column and the peppering cannot drift between call sites.
 
+mod admin_keys;
 mod audit;
 mod challenges;
 mod grin_slatepacks;

src/models/db.rs

@@ -180,6 +180,41 @@ pub struct AuditLog {
     pub created_at: DateTime<Utc>,
 }
 
+/// An admin allowlist entry. The server holds only the pubkey; `integrity_mac`
+/// binds the authorization-bearing fields so a DB-write attacker cannot silently
+/// un-revoke or revive a key. Never `Serialize` to a public surface.
+#[derive(Debug, Clone, FromRow)]
+pub struct AdminKey {
+    pub id: Uuid,
+    pub pubkey: String,
+    pub label: Option<String>,
+    pub scope: String,
+    pub created_at: DateTime<Utc>,
+    pub created_by_kind: String,
+    /// `NULL` while pending (first login not yet completed).
+    pub activated_at: Option<DateTime<Utc>>,
+    pub activation_deadline: Option<DateTime<Utc>>,
+    pub revoked_at: Option<DateTime<Utc>>,
+    pub last_used_at: Option<DateTime<Utc>>,
+    pub integrity_mac: String,
+}
+
+/// An admin session backing a short-lived admin access token. Separate table and
+/// secret from user `sessions` so the two token kinds can never be interchanged.
+#[derive(Debug, Clone, FromRow)]
+pub struct AdminSession {
+    pub id: Uuid,
+    pub admin_key_id: Uuid,
+    pub pubkey: String,
+    pub refresh_token_hash: String,
+    pub access_jti: String,
+    pub device_info: Option<String>,
+    pub ip_address: Option<IpNetwork>,
+    pub created_at: DateTime<Utc>,
+    pub expires_at: DateTime<Utc>,
+    pub revoked_at: Option<DateTime<Utc>>,
+}
+
 // ── Input structs (no auto-generated fields) ────────────────────────────────
 
 /// Input for creating a new user. Peppered values are supplied by the db layer.
@@ -234,6 +269,17 @@ pub struct NewGrinSlatepack {
     pub expires_at: DateTime<Utc>,
 }
 
+/// Input for adding an admin allowlist entry. The `id`, timestamps, and
+/// `integrity_mac` are computed by the db layer.
+#[derive(Debug, Clone)]
+pub struct NewAdminKey {
+    pub pubkey: String,
+    pub label: Option<String>,
+    pub scope: String,
+    pub created_by_kind: String,
+    pub activation_deadline: Option<DateTime<Utc>>,
+}
+
 #[derive(Debug, Clone)]
 pub struct NewAuditLog {
     pub user_id: Option<Uuid>,