diff --git a/lib/angel_security.dart b/lib/angel_security.dart
index 2f1b6977..e9a28383 100644
--- a/lib/angel_security.dart
+++ b/lib/angel_security.dart
@@ -1,2 +1,3 @@
+export 'src/in_memory_rate_limiter.dart';
 export 'src/rate_limiter.dart';
 export 'src/rate_limiting_window.dart';
\ No newline at end of file
diff --git a/lib/src/in_memory_rate_limiter.dart b/lib/src/in_memory_rate_limiter.dart
new file mode 100644
index 00000000..d545b8b6
--- /dev/null
+++ b/lib/src/in_memory_rate_limiter.dart
@@ -0,0 +1,30 @@
+import 'dart:async';
+import 'package:angel_framework/angel_framework.dart';
+import 'rate_limiter.dart';
+import 'rate_limiting_window.dart';
+
+/// A simple [RateLimiter] implementation that uses a simple in-memory map
+/// to store rate limiting information.
+class InMemoryRateLimiter<User> extends RateLimiter<User> {
+  /// A callback used to compute the current user.
+  final FutureOr<User> Function(RequestContext, ResponseContext) getUser;
+  final _cache = <User, RateLimitingWindow<User>>{};
+
+  InMemoryRateLimiter(
+      int maxPointsPerWindow, Duration windowDuration, this.getUser,
+      {String errorMessage})
+      : super(maxPointsPerWindow, windowDuration, errorMessage: errorMessage);
+
+  @override
+  FutureOr<RateLimitingWindow<User>> getCurrentWindow(
+      RequestContext req, ResponseContext res, DateTime currentTime) async {
+    var user = await getUser(req, res);
+    return _cache[user] ??= RateLimitingWindow(user, currentTime, 0);
+  }
+
+  @override
+  FutureOr<void> updateCurrentWindow(RequestContext req, ResponseContext res,
+      RateLimitingWindow<User> window, DateTime currentTime) {
+    _cache[window.user] = window;
+  }
+}
diff --git a/lib/src/rate_limiter.dart b/lib/src/rate_limiter.dart
index f450aae5..7ece0fa3 100644
--- a/lib/src/rate_limiter.dart
+++ b/lib/src/rate_limiter.dart
@@ -34,12 +34,12 @@ abstract class RateLimiter<User> {
   /// then you would return a window containing the current hour,
   /// and the number of requests the user has sent in the past hour.
   FutureOr<RateLimitingWindow<User>> getCurrentWindow(
-      RequestContext req, ResponseContext res);
+      RequestContext req, ResponseContext res, DateTime currentTime);
 
   /// Updates the underlying store with information about the new
   /// [window] that the user is operating in.
-  FutureOr<void> updateCurrentWindow(
-      RequestContext req, ResponseContext res, RateLimitingWindow<User> window);
+  FutureOr<void> updateCurrentWindow(RequestContext req, ResponseContext res,
+      RateLimitingWindow<User> window, DateTime currentTime);
 
   /// Computes the amount of points that a given request will cost. This amount
   /// is then added to the amount of points that the user has already consumed
@@ -96,11 +96,11 @@ abstract class RateLimiter<User> {
   /// [maxPointsPerWindow].
   Future handleRequest(RequestContext req, ResponseContext res) async {
     // Obtain information about the current window.
-    var currentWindow = await getCurrentWindow(req, res);
+    var now = DateTime.now().toUtc();
+    var currentWindow = await getCurrentWindow(req, res, now);
     // Check if the rate limit has been exceeded. If so, reject the request.
     // To perform this check, we must first determine whether a new window
     // has begun since the previous request.
-    var now = DateTime.now().toUtc();
     var currentWindowEnd = currentWindow.startTime.toUtc().add(windowDuration);
     // We must also compute the missing information about the current window,
     // so that we can relay that information to the client.
@@ -119,7 +119,7 @@ abstract class RateLimiter<User> {
         ..pointLimit = maxPointsPerWindow
         ..remainingPoints = remainingPoints < 0 ? 0 : remainingPoints
         ..resetTime = now.add(windowDuration);
-      await updateCurrentWindow(req, res, newWindow);
+      await updateCurrentWindow(req, res, newWindow, now);
       await sendWindowInformation(req, res, newWindow);
     }
 
@@ -143,7 +143,7 @@ abstract class RateLimiter<User> {
       if (currentWindow.remainingPoints < 0) {
         currentWindow.remainingPoints = 0;
       }
-      await updateCurrentWindow(req, res, currentWindow);
+      await updateCurrentWindow(req, res, currentWindow, now);
       await sendWindowInformation(req, res, currentWindow);
     }