security(auth): add rate limiting to token login endpoint

src/lib/utils/authRateLimit.ts

@@ -0,0 +1,89 @@
+/**
+ * Component: Auth Rate Limiting
+ * Documentation: documentation/backend/services/auth.md
+ *
+ * In-memory fixed-window rate limiter with lazy eviction and periodic sweep
+ * to prevent unbounded memory growth.
+ */
+
+type Bucket = {
+  count: number;
+  resetAt: number;
+};
+
+type RateLimitResult = {
+  allowed: boolean;
+  retryAfterSeconds: number;
+};
+
+const buckets = new Map<string, Bucket>();
+
+/** Number of checkRateLimit calls since the last full sweep */
+let checkCount = 0;
+
+/** How often (in calls) to perform a full sweep of expired buckets */
+const SWEEP_INTERVAL = 100;
+
+/**
+ * Sweep the entire bucket map and delete all expired entries.
+ * Called automatically every SWEEP_INTERVAL checks.
+ */
+function sweepExpiredBuckets(): void {
+  const now = Date.now();
+  for (const [key, bucket] of buckets) {
+    if (now >= bucket.resetAt) {
+      buckets.delete(key);
+    }
+  }
+}
+
+function checkRateLimit(key: string, maxRequests: number, windowMs: number): RateLimitResult {
+  const now = Date.now();
+
+  // Periodic full sweep every SWEEP_INTERVAL calls
+  checkCount += 1;
+  if (checkCount >= SWEEP_INTERVAL) {
+    checkCount = 0;
+    sweepExpiredBuckets();
+  }
+
+  const current = buckets.get(key);
+
+  // Lazy eviction: if the bucket is expired, delete it and start fresh
+  if (!current || now >= current.resetAt) {
+    if (current) {
+      buckets.delete(key);
+    }
+    buckets.set(key, { count: 1, resetAt: now + windowMs });
+    return { allowed: true, retryAfterSeconds: Math.ceil(windowMs / 1000) };
+  }
+
+  if (current.count >= maxRequests) {
+    return {
+      allowed: false,
+      retryAfterSeconds: Math.max(1, Math.ceil((current.resetAt - now) / 1000)),
+    };
+  }
+
+  current.count += 1;
+  return {
+    allowed: true,
+    retryAfterSeconds: Math.max(1, Math.ceil((current.resetAt - now) / 1000)),
+  };
+}
+
+/** 10 attempts per 15 minutes per IP */
+export function checkTokenLoginRateLimit(ip: string): RateLimitResult {
+  return checkRateLimit(`token-login:${ip}`, 10, 15 * 60 * 1000);
+}
+
+/** Reset all buckets and the sweep counter. For testing only. */
+export function _resetBuckets(): void {
+  buckets.clear();
+  checkCount = 0;
+}
+
+/** Get the current number of tracked buckets. For testing only. */
+export function _getBucketCount(): number {
+  return buckets.size;
+}