Azure/网络场就绪的 SecurityTokenCache

Question

我们的网站使用 ADFS 进行身份验证。为了减少每个请求的 cookie 负载，我们打开 IsSessionMode(请参阅 Your fedauth cookies on a diet)。

要使其在负载平衡环境中正常工作，我们需要做的最后一件事是实现一个农场就绪的 SecurityTokenCache。实现看起来非常简单，我主要感兴趣的是找出在处理 SecurityTokenCacheKey 以及 TryGetAllEntries 和 TryRemoveAllEntries 方法时是否应该考虑任何问题(SecurityTokenCacheKey 有 Equals 和 GetHashCode 方法的自定义实现)。

有人有这方面的例子吗？我们计划使用 AppFabric 作为后备存储，但使用任何持久存储的示例都会有所帮助 - 数据库表、Azure 表存储等。

以下是我搜索过的一些地方:

• 在 Hervey Wilson's PDC09session他用一个数据库安全 token 缓存。我还没找到样本他的 session 的代码。
• Vittorio Bertocci 优秀著作第 192 页在《Programming Windows Identity Foundation》一书中，他提到了上传Azure 就绪的 SecurityTokenCache 的示例实现书的网站。我也没有找到这个样本。

谢谢!

京东

2012 年 3 月 16 日更新 Vittorio's blog使用新的 .net 4.5 内容的示例链接:

ClaimsAwareWebFarm这个示例是对我们从你们许多人那里得到的反馈的回答:您想要一个显示场就绪 session 缓存(而不是 tokenreplycache)的示例，以便您可以通过引用使用 session 而不是交换大 cookie；您需要一种更简单的方法来保护农场中的 cookie。

Answer 1

为了提出一个有效的实现，我们最终必须使用反射器来分析 Microsoft.IdentityModel 中与 SessionSecurityToken 相关的不同类。以下是我们的想法。此实现部署在我们的开发和质量保证环境中，似乎工作正常，它对应用程序池回收等具有弹性。

在 global.asax 中:

protected void Application_Start(object sender, EventArgs e)
{
    FederatedAuthentication.ServiceConfigurationCreated += this.OnServiceConfigurationCreated;
}

private void OnServiceConfigurationCreated(object sender, ServiceConfigurationCreatedEventArgs e)
{
    var sessionTransforms = new List<CookieTransform>(new CookieTransform[]
            {
                new DeflateCookieTransform(),
                new RsaEncryptionCookieTransform(
                    e.ServiceConfiguration.ServiceCertificate),
                new RsaSignatureCookieTransform(
                    e.ServiceConfiguration.ServiceCertificate)
            });

    // following line is pseudo code.  use your own durable cache implementation.
    var durableCache = new AppFabricCacheWrapper();

    var tokenCache = new DurableSecurityTokenCache(durableCache, 5000);
    var sessionHandler = new SessionSecurityTokenHandler(sessionTransforms.AsReadOnly(),
        tokenCache,
        TimeSpan.FromDays(1));

    e.ServiceConfiguration.SecurityTokenHandlers.AddOrReplace(sessionHandler);
}

private void WSFederationAuthenticationModule_SecurityTokenValidated(object sender, SecurityTokenValidatedEventArgs e)
{
    FederatedAuthentication.SessionAuthenticationModule.IsSessionMode = true;
}

DurableSecurityTokenCache.cs:

/// <summary>
/// Two level durable security token cache (level 1: in memory MRU, level 2: out of process cache).
/// </summary>
public class DurableSecurityTokenCache : SecurityTokenCache
{
    private ICache<string, byte[]> durableCache;
    private readonly MruCache<SecurityTokenCacheKey, SecurityToken> mruCache;

    /// <summary>
    /// The constructor.
    /// </summary>
    /// <param name="durableCache">The durable second level cache (should be out of process ie sql server, azure table, app fabric, etc).</param>
    /// <param name="mruCapacity">Capacity of the internal first level cache (in-memory MRU cache).</param>
    public DurableSecurityTokenCache(ICache<string, byte[]> durableCache, int mruCapacity)
    {
        this.durableCache = durableCache;
        this.mruCache = new MruCache<SecurityTokenCacheKey, SecurityToken>(mruCapacity, mruCapacity / 4);
    }

    public override bool TryAddEntry(object key, SecurityToken value)
    {
        var cacheKey = (SecurityTokenCacheKey)key;

        // add the entry to the mru cache.
        this.mruCache.Add(cacheKey, value);

        // add the entry to the durable cache.
        var keyString = GetKeyString(cacheKey);
        var buffer = this.GetSerializer().Serialize((SessionSecurityToken)value);
        this.durableCache.Add(keyString, buffer);

        return true;
    }

    public override bool TryGetEntry(object key, out SecurityToken value)
    {
        var cacheKey = (SecurityTokenCacheKey)key;

        // attempt to retrieve the entry from the mru cache.
        value = this.mruCache.Get(cacheKey);
        if (value != null)
            return true;

        // entry wasn't in the mru cache, retrieve it from the app fabric cache.
        var keyString = GetKeyString(cacheKey);

        var buffer = this.durableCache.Get(keyString);
        var result = buffer != null;
        if (result)
        {
            // we had a cache miss in the mru cache but found the item in the durable cache...

            // deserialize the value retrieved from the durable cache.
            value = this.GetSerializer().Deserialize(buffer);

            // push this item into the mru cache.
            this.mruCache.Add(cacheKey, value);
        }

        return result;
    }

    public override bool TryRemoveEntry(object key)
    {
        var cacheKey = (SecurityTokenCacheKey)key;

        // remove the entry from the mru cache.
        this.mruCache.Remove(cacheKey);

        // remove the entry from the durable cache.
        var keyString = GetKeyString(cacheKey);
        this.durableCache.Remove(keyString);

        return true;
    }

    public override bool TryReplaceEntry(object key, SecurityToken newValue)
    {
        var cacheKey = (SecurityTokenCacheKey)key;

        // remove the entry in the mru cache.
        this.mruCache.Remove(cacheKey);

        // remove the entry in the durable cache.
        var keyString = GetKeyString(cacheKey);

        // add the new value.
        return this.TryAddEntry(key, newValue);
    }

    public override bool TryGetAllEntries(object key, out IList<SecurityToken> tokens)
    {
        // not implemented... haven't been able to find how/when this method is used.
        tokens = new List<SecurityToken>();
        return true;
        //throw new NotImplementedException();
    }

    public override bool TryRemoveAllEntries(object key)
    {
        // not implemented... haven't been able to find how/when this method is used.
        return true;
        //throw new NotImplementedException();
    }

    public override void ClearEntries()
    {
        // not implemented... haven't been able to find how/when this method is used.
        //throw new NotImplementedException();
    }

    /// <summary>
    /// Gets the string representation of the specified SecurityTokenCacheKey.
    /// </summary>
    private string GetKeyString(SecurityTokenCacheKey key)
    {
        return string.Format("{0}; {1}; {2}", key.ContextId, key.KeyGeneration, key.EndpointId);
    }

    /// <summary>
    /// Gets a new instance of the token serializer.
    /// </summary>
    private SessionSecurityTokenCookieSerializer GetSerializer()
    {
        return new SessionSecurityTokenCookieSerializer();  // may need to do something about handling bootstrap tokens.
    }
}

MruCache.cs:

/// <summary>
/// Most recently used (MRU) cache.
/// </summary>
/// <typeparam name="TKey">The key type.</typeparam>
/// <typeparam name="TValue">The value type.</typeparam>
public class MruCache<TKey, TValue> : ICache<TKey, TValue>
{
    private Dictionary<TKey, TValue> mruCache;
    private LinkedList<TKey> mruList;
    private object syncRoot;
    private int capacity;
    private int sizeAfterPurge;

    /// <summary>
    /// The constructor.
    /// </summary>
    /// <param name="capacity">The capacity.</param>
    /// <param name="sizeAfterPurge">Size to make the cache after purging because it's reached capacity.</param>
    public MruCache(int capacity, int sizeAfterPurge)
    {
        this.mruList = new LinkedList<TKey>();
        this.mruCache = new Dictionary<TKey, TValue>(capacity);
        this.capacity = capacity;
        this.sizeAfterPurge = sizeAfterPurge;
        this.syncRoot = new object();
    }

    /// <summary>
    /// Adds an item if it doesn't already exist.
    /// </summary>
    public void Add(TKey key, TValue value)
    {
        lock (this.syncRoot)
        {
            if (mruCache.ContainsKey(key))
                return;

            if (mruCache.Count + 1 >= this.capacity)
            {
                while (mruCache.Count > this.sizeAfterPurge)
                {
                    var lru = mruList.Last.Value;
                    mruCache.Remove(lru);
                    mruList.RemoveLast();
                }
            }
            mruCache.Add(key, value);
            mruList.AddFirst(key);
        }
    }

    /// <summary>
    /// Removes an item if it exists.
    /// </summary>
    public void Remove(TKey key)
    {
        lock (this.syncRoot)
        {
            if (!mruCache.ContainsKey(key))
                return;

            mruCache.Remove(key);
            mruList.Remove(key);
        }
    }

    /// <summary>
    /// Gets an item.  If a matching item doesn't exist null is returned.
    /// </summary>
    public TValue Get(TKey key)
    {
        lock (this.syncRoot)
        {
            if (!mruCache.ContainsKey(key))
                return default(TValue);

            mruList.Remove(key);
            mruList.AddFirst(key);
            return mruCache[key];
        }
    }

    /// <summary>
    /// Gets whether a key is contained in the cache.
    /// </summary>
    public bool ContainsKey(TKey key)
    {
        lock (this.syncRoot)
            return mruCache.ContainsKey(key);
    }
}

ICache.cs:

/// <summary>
/// A cache.
/// </summary>
/// <typeparam name="TKey">The key type.</typeparam>
/// <typeparam name="TValue">The value type.</typeparam>
public interface ICache<TKey, TValue>
{
    void Add(TKey key, TValue value);
    void Remove(TKey key);
    TValue Get(TKey key);
}