feat: implement user authentication system with admin dashboard

src/web/admin.rs

@@ -0,0 +1,205 @@
+//! Admin API handlers.
+//!
+//! All endpoints require the `AdminUser` extractor, returning 401/403 as needed.
+
+use axum::extract::{Path, State};
+use axum::http::StatusCode;
+use axum::response::Json;
+use serde::Deserialize;
+use serde_json::{Value, json};
+
+use crate::data::models::User;
+use crate::state::AppState;
+use crate::web::extractors::AdminUser;
+
+/// `GET /api/admin/status` — Enhanced system status for admins.
+pub async fn admin_status(
+    AdminUser(_user): AdminUser,
+    State(state): State<AppState>,
+) -> Result<Json<Value>, (StatusCode, Json<Value>)> {
+    let (user_count,): (i64,) = sqlx::query_as("SELECT COUNT(*) FROM users")
+        .fetch_one(&state.db_pool)
+        .await
+        .map_err(|e| {
+            tracing::error!(error = %e, "failed to count users");
+            (
+                StatusCode::INTERNAL_SERVER_ERROR,
+                Json(json!({"error": "failed to count users"})),
+            )
+        })?;
+
+    let (session_count,): (i64,) =
+        sqlx::query_as("SELECT COUNT(*) FROM user_sessions WHERE expires_at > now()")
+            .fetch_one(&state.db_pool)
+            .await
+            .map_err(|e| {
+                tracing::error!(error = %e, "failed to count sessions");
+                (
+                    StatusCode::INTERNAL_SERVER_ERROR,
+                    Json(json!({"error": "failed to count sessions"})),
+                )
+            })?;
+
+    let course_count = state.get_course_count().await.map_err(|e| {
+        tracing::error!(error = %e, "failed to count courses");
+        (
+            StatusCode::INTERNAL_SERVER_ERROR,
+            Json(json!({"error": "failed to count courses"})),
+        )
+    })?;
+
+    let (scrape_job_count,): (i64,) = sqlx::query_as("SELECT COUNT(*) FROM scrape_jobs")
+        .fetch_one(&state.db_pool)
+        .await
+        .map_err(|e| {
+            tracing::error!(error = %e, "failed to count scrape jobs");
+            (
+                StatusCode::INTERNAL_SERVER_ERROR,
+                Json(json!({"error": "failed to count scrape jobs"})),
+            )
+        })?;
+
+    let services: Vec<Value> = state
+        .service_statuses
+        .all()
+        .into_iter()
+        .map(|(name, status)| {
+            json!({
+                "name": name,
+                "status": status,
+            })
+        })
+        .collect();
+
+    Ok(Json(json!({
+        "userCount": user_count,
+        "sessionCount": session_count,
+        "courseCount": course_count,
+        "scrapeJobCount": scrape_job_count,
+        "services": services,
+    })))
+}
+
+/// `GET /api/admin/users` — List all users.
+pub async fn list_users(
+    AdminUser(_user): AdminUser,
+    State(state): State<AppState>,
+) -> Result<Json<Vec<User>>, (StatusCode, Json<Value>)> {
+    let users = crate::data::users::list_users(&state.db_pool)
+        .await
+        .map_err(|e| {
+            tracing::error!(error = %e, "failed to list users");
+            (
+                StatusCode::INTERNAL_SERVER_ERROR,
+                Json(json!({"error": "failed to list users"})),
+            )
+        })?;
+
+    Ok(Json(users))
+}
+
+#[derive(Deserialize)]
+pub struct SetAdminBody {
+    is_admin: bool,
+}
+
+/// `PUT /api/admin/users/{discord_id}/admin` — Set admin status for a user.
+pub async fn set_user_admin(
+    AdminUser(_user): AdminUser,
+    State(state): State<AppState>,
+    Path(discord_id): Path<i64>,
+    Json(body): Json<SetAdminBody>,
+) -> Result<Json<User>, (StatusCode, Json<Value>)> {
+    let user = crate::data::users::set_admin(&state.db_pool, discord_id, body.is_admin)
+        .await
+        .map_err(|e| {
+            tracing::error!(error = %e, "failed to set admin status");
+            (
+                StatusCode::INTERNAL_SERVER_ERROR,
+                Json(json!({"error": "failed to set admin status"})),
+            )
+        })?
+        .ok_or_else(|| {
+            (
+                StatusCode::NOT_FOUND,
+                Json(json!({"error": "user not found"})),
+            )
+        })?;
+
+    state.session_cache.evict_user(discord_id);
+
+    Ok(Json(user))
+}
+
+/// `GET /api/admin/scrape-jobs` — List scrape jobs.
+pub async fn list_scrape_jobs(
+    AdminUser(_user): AdminUser,
+    State(state): State<AppState>,
+) -> Result<Json<Value>, (StatusCode, Json<Value>)> {
+    let rows = sqlx::query_as::<_, crate::data::models::ScrapeJob>(
+        "SELECT * FROM scrape_jobs ORDER BY priority DESC, execute_at ASC LIMIT 100",
+    )
+    .fetch_all(&state.db_pool)
+    .await
+    .map_err(|e| {
+        tracing::error!(error = %e, "failed to list scrape jobs");
+        (
+            StatusCode::INTERNAL_SERVER_ERROR,
+            Json(json!({"error": "failed to list scrape jobs"})),
+        )
+    })?;
+
+    let jobs: Vec<Value> = rows
+        .iter()
+        .map(|j| {
+            json!({
+                "id": j.id,
+                "targetType": format!("{:?}", j.target_type),
+                "targetPayload": j.target_payload,
+                "priority": format!("{:?}", j.priority),
+                "executeAt": j.execute_at.to_rfc3339(),
+                "createdAt": j.created_at.to_rfc3339(),
+                "lockedAt": j.locked_at.map(|t| t.to_rfc3339()),
+                "retryCount": j.retry_count,
+                "maxRetries": j.max_retries,
+            })
+        })
+        .collect();
+
+    Ok(Json(json!({ "jobs": jobs })))
+}
+
+/// `GET /api/admin/audit-log` — List recent audit entries.
+pub async fn list_audit_log(
+    AdminUser(_user): AdminUser,
+    State(state): State<AppState>,
+) -> Result<Json<Value>, (StatusCode, Json<Value>)> {
+    let rows = sqlx::query_as::<_, crate::data::models::CourseAudit>(
+        "SELECT * FROM course_audits ORDER BY timestamp DESC LIMIT 200",
+    )
+    .fetch_all(&state.db_pool)
+    .await
+    .map_err(|e| {
+        tracing::error!(error = %e, "failed to list audit log");
+        (
+            StatusCode::INTERNAL_SERVER_ERROR,
+            Json(json!({"error": "failed to list audit log"})),
+        )
+    })?;
+
+    let entries: Vec<Value> = rows
+        .iter()
+        .map(|a| {
+            json!({
+                "id": a.id,
+                "courseId": a.course_id,
+                "timestamp": a.timestamp.to_rfc3339(),
+                "fieldChanged": a.field_changed,
+                "oldValue": a.old_value,
+                "newValue": a.new_value,
+            })
+        })
+        .collect();
+
+    Ok(Json(json!({ "entries": entries })))
+}

src/web/auth.rs

@@ -0,0 +1,300 @@
+//! Discord OAuth2 authentication handlers.
+//!
+//! Provides login, callback, logout, and session introspection endpoints
+//! for Discord OAuth2 authentication flow.
+
+use axum::extract::{Extension, Query, State};
+use axum::http::{HeaderMap, StatusCode, header};
+use axum::response::{IntoResponse, Json, Redirect, Response};
+use serde::Deserialize;
+use serde_json::{Value, json};
+use std::time::Duration;
+use tracing::{error, info, warn};
+
+use crate::state::AppState;
+
+/// OAuth configuration passed as an Axum Extension.
+#[derive(Clone)]
+pub struct AuthConfig {
+    pub client_id: String,
+    pub client_secret: String,
+    /// Optional base URL override (e.g. "https://banner.xevion.dev").
+    /// When `None`, the redirect URI is derived from the request's Origin/Host header.
+    pub redirect_base: Option<String>,
+}
+
+const CALLBACK_PATH: &str = "/api/auth/callback";
+
+/// Derive the origin (scheme + host + port) the user's browser is actually on.
+///
+/// Priority:
+/// 1. Configured `redirect_base` (production override)
+/// 2. `Referer` header — preserves the real browser origin even through
+///    reverse proxies that rewrite `Host` (e.g. Vite dev proxy with
+///    `changeOrigin: true`)
+/// 3. `Origin` header (present on POST / CORS requests)
+/// 4. `Host` header (last resort, may be rewritten by proxies)
+fn resolve_origin(auth_config: &AuthConfig, headers: &HeaderMap) -> String {
+    if let Some(base) = &auth_config.redirect_base {
+        return base.trim_end_matches('/').to_owned();
+    }
+
+    // Referer carries the full browser URL; extract just the origin.
+    if let Some(referer) = headers.get(header::REFERER).and_then(|v| v.to_str().ok())
+        && let Ok(parsed) = url::Url::parse(referer)
+    {
+        let origin = parsed.origin().unicode_serialization();
+        if origin != "null" {
+            return origin;
+        }
+    }
+
+    if let Some(origin) = headers.get("origin").and_then(|v| v.to_str().ok()) {
+        return origin.trim_end_matches('/').to_owned();
+    }
+
+    if let Some(host) = headers.get(header::HOST).and_then(|v| v.to_str().ok()) {
+        return format!("http://{host}");
+    }
+
+    "http://localhost:8080".to_owned()
+}
+
+#[derive(Deserialize)]
+pub struct CallbackParams {
+    code: String,
+    state: String,
+}
+
+#[derive(Deserialize)]
+struct TokenResponse {
+    access_token: String,
+}
+
+#[derive(Deserialize)]
+struct DiscordUser {
+    id: String,
+    username: String,
+    avatar: Option<String>,
+}
+
+/// Extract the `session` cookie value from request headers.
+fn extract_session_token(headers: &HeaderMap) -> Option<String> {
+    headers
+        .get(header::COOKIE)?
+        .to_str()
+        .ok()?
+        .split(';')
+        .find_map(|cookie| {
+            let cookie = cookie.trim();
+            cookie.strip_prefix("session=").map(|v| v.to_owned())
+        })
+}
+
+/// Build a `Set-Cookie` header value for the session cookie.
+fn session_cookie(token: &str, max_age: i64, secure: bool) -> String {
+    let mut cookie = format!("session={token}; HttpOnly; SameSite=Lax; Path=/; Max-Age={max_age}");
+    if secure {
+        cookie.push_str("; Secure");
+    }
+    cookie
+}
+
+/// `GET /api/auth/login` — Redirect to Discord OAuth2 authorization page.
+pub async fn auth_login(
+    State(state): State<AppState>,
+    Extension(auth_config): Extension<AuthConfig>,
+    headers: HeaderMap,
+) -> Redirect {
+    let origin = resolve_origin(&auth_config, &headers);
+    let redirect_uri = format!("{origin}{CALLBACK_PATH}");
+    let csrf_state = state.oauth_state_store.generate(origin);
+    let redirect_uri_encoded = urlencoding::encode(&redirect_uri);
+
+    let url = format!(
+        "https://discord.com/oauth2/authorize\
+         ?client_id={}\
+         &redirect_uri={redirect_uri_encoded}\
+         &response_type=code\
+         &scope=identify\
+         &state={csrf_state}",
+        auth_config.client_id,
+    );
+
+    Redirect::temporary(&url)
+}
+
+/// `GET /api/auth/callback` — Handle Discord OAuth2 callback.
+pub async fn auth_callback(
+    State(state): State<AppState>,
+    Extension(auth_config): Extension<AuthConfig>,
+    Query(params): Query<CallbackParams>,
+) -> Result<Response, (StatusCode, Json<Value>)> {
+    // 1. Validate CSRF state and recover the origin used during login
+    let origin = state
+        .oauth_state_store
+        .validate(&params.state)
+        .ok_or_else(|| {
+            warn!("OAuth callback with invalid CSRF state");
+            (
+                StatusCode::BAD_REQUEST,
+                Json(json!({ "error": "Invalid OAuth state" })),
+            )
+        })?;
+
+    // 2. Exchange authorization code for access token
+    let redirect_uri = format!("{origin}{CALLBACK_PATH}");
+    let client = reqwest::Client::new();
+    let token_response = client
+        .post("https://discord.com/api/oauth2/token")
+        .form(&[
+            ("client_id", auth_config.client_id.as_str()),
+            ("client_secret", auth_config.client_secret.as_str()),
+            ("grant_type", "authorization_code"),
+            ("code", params.code.as_str()),
+            ("redirect_uri", redirect_uri.as_str()),
+        ])
+        .send()
+        .await
+        .map_err(|e| {
+            error!(error = %e, "failed to exchange OAuth code for token");
+            (
+                StatusCode::BAD_GATEWAY,
+                Json(json!({ "error": "Failed to exchange code with Discord" })),
+            )
+        })?;
+
+    if !token_response.status().is_success() {
+        let status = token_response.status();
+        let body = token_response.text().await.unwrap_or_default();
+        error!(%status, %body, "Discord token exchange returned error");
+        return Err((
+            StatusCode::BAD_GATEWAY,
+            Json(json!({ "error": "Discord token exchange failed" })),
+        ));
+    }
+
+    let token_data: TokenResponse = token_response.json().await.map_err(|e| {
+        error!(error = %e, "failed to parse Discord token response");
+        (
+            StatusCode::BAD_GATEWAY,
+            Json(json!({ "error": "Invalid token response from Discord" })),
+        )
+    })?;
+
+    // 3. Fetch Discord user profile
+    let discord_user: DiscordUser = client
+        .get("https://discord.com/api/users/@me")
+        .bearer_auth(&token_data.access_token)
+        .send()
+        .await
+        .map_err(|e| {
+            error!(error = %e, "failed to fetch Discord user profile");
+            (
+                StatusCode::BAD_GATEWAY,
+                Json(json!({ "error": "Failed to fetch Discord profile" })),
+            )
+        })?
+        .json()
+        .await
+        .map_err(|e| {
+            error!(error = %e, "failed to parse Discord user profile");
+            (
+                StatusCode::BAD_GATEWAY,
+                Json(json!({ "error": "Invalid user profile from Discord" })),
+            )
+        })?;
+
+    let discord_id: i64 = discord_user.id.parse().map_err(|_| {
+        error!(id = %discord_user.id, "Discord user ID is not a valid i64");
+        (
+            StatusCode::BAD_GATEWAY,
+            Json(json!({ "error": "Invalid Discord user ID" })),
+        )
+    })?;
+
+    // 4. Upsert user
+    let user = crate::data::users::upsert_user(
+        &state.db_pool,
+        discord_id,
+        &discord_user.username,
+        discord_user.avatar.as_deref(),
+    )
+    .await
+    .map_err(|e| {
+        error!(error = %e, "failed to upsert user");
+        (
+            StatusCode::INTERNAL_SERVER_ERROR,
+            Json(json!({ "error": "Database error" })),
+        )
+    })?;
+
+    info!(discord_id, username = %user.discord_username, "user authenticated via OAuth");
+
+    // 5. Create session
+    let session = crate::data::sessions::create_session(
+        &state.db_pool,
+        discord_id,
+        Duration::from_secs(7 * 24 * 3600),
+    )
+    .await
+    .map_err(|e| {
+        error!(error = %e, "failed to create session");
+        (
+            StatusCode::INTERNAL_SERVER_ERROR,
+            Json(json!({ "error": "Failed to create session" })),
+        )
+    })?;
+
+    // 6. Build response with session cookie
+    let secure = redirect_uri.starts_with("https://");
+    let cookie = session_cookie(&session.id, 604800, secure);
+
+    let redirect_to = if user.is_admin { "/admin" } else { "/" };
+
+    Ok((
+        [(header::SET_COOKIE, cookie)],
+        Redirect::temporary(redirect_to),
+    )
+        .into_response())
+}
+
+/// `POST /api/auth/logout` — Destroy the current session.
+pub async fn auth_logout(State(state): State<AppState>, headers: HeaderMap) -> Response {
+    if let Some(token) = extract_session_token(&headers) {
+        if let Err(e) = crate::data::sessions::delete_session(&state.db_pool, &token).await {
+            warn!(error = %e, "failed to delete session from database");
+        }
+        state.session_cache.evict(&token);
+    }
+
+    let cookie = session_cookie("", 0, false);
+
+    (
+        StatusCode::OK,
+        [(header::SET_COOKIE, cookie)],
+        Json(json!({ "ok": true })),
+    )
+        .into_response()
+}
+
+/// `GET /api/auth/me` — Return the current authenticated user's info.
+pub async fn auth_me(
+    State(state): State<AppState>,
+    headers: HeaderMap,
+) -> Result<Json<Value>, StatusCode> {
+    let token = extract_session_token(&headers).ok_or(StatusCode::UNAUTHORIZED)?;
+
+    let user = state
+        .session_cache
+        .get_user(&token)
+        .await
+        .ok_or(StatusCode::UNAUTHORIZED)?;
+
+    Ok(Json(json!({
+        "discordId": user.discord_id.to_string(),
+        "username": user.discord_username,
+        "avatarHash": user.discord_avatar_hash,
+        "isAdmin": user.is_admin,
+    })))
+}

src/web/extractors.rs

@@ -0,0 +1,74 @@
+//! Axum extractors for authentication and authorization.
+
+use axum::extract::FromRequestParts;
+use axum::http::{StatusCode, header};
+use axum::response::Json;
+use http::request::Parts;
+use serde_json::json;
+
+use crate::data::models::User;
+use crate::state::AppState;
+
+/// Extractor that resolves the session cookie to an authenticated [`User`].
+///
+/// Returns 401 if no valid session cookie is present.
+pub struct AuthUser(pub User);
+
+impl FromRequestParts<AppState> for AuthUser {
+    type Rejection = (StatusCode, Json<serde_json::Value>);
+
+    async fn from_request_parts(
+        parts: &mut Parts,
+        state: &AppState,
+    ) -> Result<Self, Self::Rejection> {
+        let token = parts
+            .headers
+            .get(header::COOKIE)
+            .and_then(|v| v.to_str().ok())
+            .and_then(|cookies| {
+                cookies
+                    .split(';')
+                    .find_map(|c| c.trim().strip_prefix("session=").map(|v| v.to_owned()))
+            })
+            .ok_or_else(|| {
+                (
+                    StatusCode::UNAUTHORIZED,
+                    Json(json!({"error": "unauthorized", "message": "No session cookie"})),
+                )
+            })?;
+
+        let user = state.session_cache.get_user(&token).await.ok_or_else(|| {
+            (
+                StatusCode::UNAUTHORIZED,
+                Json(json!({"error": "unauthorized", "message": "Invalid or expired session"})),
+            )
+        })?;
+
+        Ok(AuthUser(user))
+    }
+}
+
+/// Extractor that requires an authenticated admin user.
+///
+/// Returns 401 if not authenticated, 403 if not admin.
+pub struct AdminUser(pub User);
+
+impl FromRequestParts<AppState> for AdminUser {
+    type Rejection = (StatusCode, Json<serde_json::Value>);
+
+    async fn from_request_parts(
+        parts: &mut Parts,
+        state: &AppState,
+    ) -> Result<Self, Self::Rejection> {
+        let AuthUser(user) = AuthUser::from_request_parts(parts, state).await?;
+
+        if !user.is_admin {
+            return Err((
+                StatusCode::FORBIDDEN,
+                Json(json!({"error": "forbidden", "message": "Admin access required"})),
+            ));
+        }
+
+        Ok(AdminUser(user))
+    }
+}

src/web/mod.rs

@@ -1,7 +1,11 @@
 //! Web API module for the banner application.
 
+pub mod admin;
 #[cfg(feature = "embed-assets")]
 pub mod assets;
+pub mod auth;
+pub mod extractors;
 pub mod routes;
+pub mod session_cache;
 
 pub use routes::*;

src/web/routes.rs

@@ -1,13 +1,16 @@
 //! Web API endpoints for Banner bot monitoring and metrics.
 
 use axum::{
-    Router,
+    Extension, Router,
     body::Body,
     extract::{Path, Query, Request, State},
     http::StatusCode as AxumStatusCode,
     response::{Json, Response},
-    routing::get,
+    routing::{get, post, put},
 };
+
+use crate::web::admin;
+use crate::web::auth::{self, AuthConfig};
 #[cfg(feature = "embed-assets")]
 use axum::{
     http::{HeaderMap, HeaderValue, StatusCode, Uri},
@@ -68,7 +71,7 @@ fn set_caching_headers(response: &mut Response, path: &str, etag: &str) {
 }
 
 /// Creates the web server router
-pub fn create_router(app_state: AppState) -> Router {
+pub fn create_router(app_state: AppState, auth_config: AuthConfig) -> Router {
     let api_router = Router::new()
         .route("/health", get(health))
         .route("/status", get(status))
@@ -78,9 +81,31 @@ pub fn create_router(app_state: AppState) -> Router {
         .route("/terms", get(get_terms))
         .route("/subjects", get(get_subjects))
         .route("/reference/{category}", get(get_reference))
+        .with_state(app_state.clone());
+
+    let auth_router = Router::new()
+        .route("/auth/login", get(auth::auth_login))
+        .route("/auth/callback", get(auth::auth_callback))
+        .route("/auth/logout", post(auth::auth_logout))
+        .route("/auth/me", get(auth::auth_me))
+        .layer(Extension(auth_config))
+        .with_state(app_state.clone());
+
+    let admin_router = Router::new()
+        .route("/admin/status", get(admin::admin_status))
+        .route("/admin/users", get(admin::list_users))
+        .route(
+            "/admin/users/{discord_id}/admin",
+            put(admin::set_user_admin),
+        )
+        .route("/admin/scrape-jobs", get(admin::list_scrape_jobs))
+        .route("/admin/audit-log", get(admin::list_audit_log))
         .with_state(app_state);
 
-    let mut router = Router::new().nest("/api", api_router);
+    let mut router = Router::new()
+        .nest("/api", api_router)
+        .nest("/api", auth_router)
+        .nest("/api", admin_router);
 
     // When embed-assets feature is enabled, serve embedded static assets
     #[cfg(feature = "embed-assets")]

src/web/session_cache.rs

@@ -0,0 +1,188 @@
+//! In-memory caches for session resolution and OAuth CSRF state.
+
+use chrono::{DateTime, Utc};
+use dashmap::DashMap;
+use rand::Rng;
+use sqlx::PgPool;
+use std::sync::Arc;
+use std::time::{Duration, Instant};
+
+use crate::data::models::User;
+
+/// Cached session entry with TTL.
+#[derive(Debug, Clone)]
+struct CachedSession {
+    user: User,
+    session_expires_at: DateTime<Utc>,
+    cached_at: Instant,
+}
+
+/// In-memory session cache backed by PostgreSQL.
+///
+/// Provides fast session resolution without a DB round-trip on every request.
+/// Cache entries expire after a configurable TTL (default 5 minutes).
+#[derive(Clone)]
+pub struct SessionCache {
+    cache: Arc<DashMap<String, CachedSession>>,
+    db_pool: PgPool,
+    cache_ttl: Duration,
+}
+
+impl SessionCache {
+    /// Create a new session cache with a 5-minute default TTL.
+    pub fn new(db_pool: PgPool) -> Self {
+        Self {
+            cache: Arc::new(DashMap::new()),
+            db_pool,
+            cache_ttl: Duration::from_secs(5 * 60),
+        }
+    }
+
+    /// Resolve a session token to a [`User`], using the cache when possible.
+    ///
+    /// On cache hit (entry present, not stale, session not expired), returns the
+    /// cached user immediately. On miss or stale entry, queries the database for
+    /// the session and user, populates the cache, and fire-and-forgets a
+    /// `touch_session` call to update `last_active_at`.
+    pub async fn get_user(&self, token: &str) -> Option<User> {
+        // Check cache first
+        if let Some(entry) = self.cache.get(token) {
+            let now_instant = Instant::now();
+            let now_utc = Utc::now();
+
+            let cache_fresh = entry.cached_at + self.cache_ttl > now_instant;
+            let session_valid = entry.session_expires_at > now_utc;
+
+            if cache_fresh && session_valid {
+                return Some(entry.user.clone());
+            }
+
+            // Stale or expired — drop the ref before removing
+            drop(entry);
+            self.cache.remove(token);
+        }
+
+        // Cache miss — query DB
+        let session = crate::data::sessions::get_session(&self.db_pool, token)
+            .await
+            .ok()
+            .flatten()?;
+
+        let user = crate::data::users::get_user(&self.db_pool, session.user_id)
+            .await
+            .ok()
+            .flatten()?;
+
+        self.cache.insert(
+            token.to_owned(),
+            CachedSession {
+                user: user.clone(),
+                session_expires_at: session.expires_at,
+                cached_at: Instant::now(),
+            },
+        );
+
+        // Fire-and-forget touch to update last_active_at
+        let pool = self.db_pool.clone();
+        let token_owned = token.to_owned();
+        tokio::spawn(async move {
+            if let Err(e) = crate::data::sessions::touch_session(&pool, &token_owned).await {
+                tracing::warn!(error = %e, "failed to touch session");
+            }
+        });
+
+        Some(user)
+    }
+
+    /// Remove a single session from the cache (e.g. on logout).
+    pub fn evict(&self, token: &str) {
+        self.cache.remove(token);
+    }
+
+    /// Remove all cached sessions belonging to a user.
+    pub fn evict_user(&self, discord_id: i64) {
+        self.cache
+            .retain(|_, entry| entry.user.discord_id != discord_id);
+    }
+
+    /// Delete expired sessions from the database and sweep the in-memory cache.
+    ///
+    /// Returns the number of sessions deleted from the database.
+    #[allow(dead_code)] // Intended for periodic cleanup task (not yet wired)
+    pub async fn cleanup_expired(&self) -> anyhow::Result<u64> {
+        let deleted = crate::data::sessions::cleanup_expired(&self.db_pool).await?;
+
+        let now = Utc::now();
+        self.cache.retain(|_, entry| entry.session_expires_at > now);
+
+        Ok(deleted)
+    }
+}
+
+/// Data stored alongside each OAuth CSRF state token.
+struct OAuthStateEntry {
+    created_at: Instant,
+    /// The browser origin that initiated the login flow, so the callback
+    /// can reconstruct the exact redirect_uri Discord expects.
+    origin: String,
+}
+
+/// Ephemeral store for OAuth CSRF state tokens.
+///
+/// Tokens are stored with creation time and expire after a configurable TTL.
+/// Each token is single-use: validation consumes it.
+#[derive(Clone)]
+pub struct OAuthStateStore {
+    states: Arc<DashMap<String, OAuthStateEntry>>,
+    ttl: Duration,
+}
+
+impl Default for OAuthStateStore {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl OAuthStateStore {
+    /// Create a new store with a 10-minute TTL.
+    pub fn new() -> Self {
+        Self {
+            states: Arc::new(DashMap::new()),
+            ttl: Duration::from_secs(10 * 60),
+        }
+    }
+
+    /// Generate a random 16-byte hex CSRF token, store it with the given
+    /// origin, and return the token.
+    pub fn generate(&self, origin: String) -> String {
+        let bytes: [u8; 16] = rand::rng().random();
+        let token: String = bytes.iter().map(|b| format!("{b:02x}")).collect();
+        self.states.insert(
+            token.clone(),
+            OAuthStateEntry {
+                created_at: Instant::now(),
+                origin,
+            },
+        );
+        token
+    }
+
+    /// Validate and consume a CSRF token. Returns the stored origin if the
+    /// token was present and not expired.
+    pub fn validate(&self, state: &str) -> Option<String> {
+        let (_, entry) = self.states.remove(state)?;
+        if entry.created_at.elapsed() < self.ttl {
+            Some(entry.origin)
+        } else {
+            None
+        }
+    }
+
+    /// Remove all expired entries from the store.
+    #[allow(dead_code)] // Intended for periodic cleanup task (not yet wired)
+    pub fn cleanup(&self) {
+        let ttl = self.ttl;
+        self.states
+            .retain(|_, entry| entry.created_at.elapsed() < ttl);
+    }
+}