Initial commit

MealPlan.Api/Services/InMemoryRefreshTokenStore.cs

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+using System.Collections.Concurrent;
+using MealPlan.Api.Models;
+
+namespace MealPlan.Api.Services;
+
+/// <summary>
+/// Thread-safe in-memory refresh token store registered as a singleton.
+/// Note: tokens live only for the lifetime of the process. For multi-instance
+/// deployments this should be swapped for a shared store (e.g. Redis), but it
+/// satisfies the "do not modify the database" constraint of this project.
+/// </summary>
+public class InMemoryRefreshTokenStore : IRefreshTokenStore
+{
+    private readonly ConcurrentDictionary<string, RefreshToken> _tokens = new();
+
+    public void Add(RefreshToken token) => _tokens[token.Token] = token;
+
+    public RefreshToken? Get(string token) =>
+        _tokens.TryGetValue(token, out var found) ? found : null;
+
+    public RefreshToken? Revoke(string token)
+    {
+        if (!_tokens.TryGetValue(token, out var found))
+        {
+            return null;
+        }
+
+        var wasActive = found.IsActive;
+        found.IsRevoked = true;
+        return wasActive ? found : null;
+    }
+
+    public void RemoveExpired()
+    {
+        foreach (var kvp in _tokens)
+        {
+            if (kvp.Value.IsRevoked || DateTime.UtcNow >= kvp.Value.ExpiresAtUtc)
+            {
+                _tokens.TryRemove(kvp.Key, out _);
+            }
+        }
+    }
+}