使用 Azure 缓存（.NET MVC3 应用程序）时，为什么无法组合 [Authorize] 和 [OutputCache] 属性？

使用 Windows Azure 的Microsoft.Web.DistributedCache.DistributedCacheOutputCacheProvider作为 MVC3 应用程序的 outputCache 提供程序。下面是相关的操作方法：

[ActionName("sample-cached-page")]
[OutputCache(Duration = 300, VaryByCustom = "User", 
    Location = OutputCacheLocation.Server)]
[Authorize(Users = "[email protected] /cdn-cgi/l/email-protection,[email protected] /cdn-cgi/l/email-protection")]
public virtual ActionResult SampleCachedPage()
{
    return View();
}

从网络浏览器加载此视图时出现以下异常：

System.Configuration.Provider.ProviderException: When using a custom output cache provider like 'DistributedCache', only the following expiration policies and cache features are supported: file dependencies, absolute expirations, static validation callbacks and static substitution callbacks.

System.Configuration.Provider.ProviderException: When using a custom output cache provider like 'DistributedCache', only the following expiration policies and cache features are supported:  file dependencies, absolute expirations, static validation callbacks and static substitution callbacks.
   at System.Web.Caching.OutputCache.InsertResponse(String cachedVaryKey, CachedVary cachedVary, String rawResponseKey, CachedRawResponse rawResponse, CacheDependency dependencies, DateTime absExp, TimeSpan slidingExp)
   at System.Web.Caching.OutputCacheModule.OnLeave(Object source, EventArgs eventArgs)
   at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

如果我删除 [Authorize] 属性，视图将按预期进行缓存。这是否意味着我无法将 [OutputCache] 放在必须具有 [Authorize] 的操作方法上？或者，我是否需要使用对缓存使用静态验证回调方法的自定义实现来重写 AuthorizeAttribute？

Update 1

在Evan回答之后，我在IIS Express（Azure之外）中测试了上述操作方法。以下是我对 OutputCache 属性上的 VaryByCustom = "User" 属性的覆盖：

public override string GetVaryByCustomString(HttpContext context, string custom)
{
    return "User".Equals(custom, StringComparison.OrdinalIgnoreCase)
        ? Thread.CurrentPrincipal.Identity.Name
        : base.GetVaryByCustomString(context, custom);
}

当我访问示例缓存页面时[电子邮件受保护] /cdn-cgi/l/email-protection，页面的输出被缓存，并且视图显示“此页面于 12/31/2011 11:06 被缓存：12AM (UTC)”。如果我随后注销并以身份登录[电子邮件受保护] /cdn-cgi/l/email-protection访问该页面，显示“此页面已于 12/31/2011 11:06 缓存：38AM (UTC)”。重新登录为[电子邮件受保护] /cdn-cgi/l/email-protection重新访问该页面会导致缓存显示“此页面已于 12/31/2011 11:06 缓存：12再次尝试“AM (UTC)”。进一步的登录/注销尝试显示，根据用户的不同，正在缓存和返回不同的输出。

这让我相信输出是根据用户单独缓存的，这就是我的 VaryByCustom =“User”设置和覆盖的意图。问题是它不能与 Azure 的分布式缓存提供程序一起使用。埃文，您关于仅缓存公共内容的回答仍然有效吗？

Update 2

我挖掘了源代码，发现开箱即用的 AuthorizeAttribute 实际上确实有一个非静态验证回调。这是摘录自OnAuthorization:

if (AuthorizeCore(filterContext.HttpContext)) {
    // ** IMPORTANT **
    // Since we're performing authorization at the action level, the authorization code runs
    // after the output caching module. In the worst case this could allow an authorized user
    // to cause the page to be cached, then an unauthorized user would later be served the
    // cached page. We work around this by telling proxies not to cache the sensitive page,
    // then we hook our custom authorization code into the caching mechanism so that we have
    // the final say on whether a page should be served from the cache.

    HttpCachePolicyBase cachePolicy = filterContext.HttpContext.Response.Cache;
    cachePolicy.SetProxyMaxAge(new TimeSpan(0));
    cachePolicy.AddValidationCallback(CacheValidateHandler, null /* data */);
}
else {
    HandleUnauthorizedRequest(filterContext);
}

CacheValidationHandler将缓存验证委托给protected virtual HttpValidationStatus OnCacheAuthorization(HttpContextBase)，这当然不是静态的。它不是静态的原因之一是，正如上面重要注释中所述，它调用protected virtual bool AuthorizeCore(HttpContextBase).

为了通过静态缓存验证回调方法执行任何 AuthorizeCore 逻辑，需要了解 AuthorizeAttribute 实例的 Users 和 Roles 属性。然而，似乎没有一种简单的插入方法。我必须重写 OnAuthorization 将这两个值放入 HttpContext （Items 集合？），然后重写 OnCacheAuthorization 将它们取出。但那味道很脏。

如果我们小心地在 OutputCache 属性中使用 VaryByCustom = "User" 属性，我们是否可以重写 OnCacheAuthorization 以始终返回 HttpValidationStatus.Valid？当操作方法没有 OutputCache 属性时，我们不需要担心调用此回调，对吗？如果我们确实有一个没有 VaryByCustom = "User" 的 OutputCache 属性，那么很明显，无论哪个用户请求创建了缓存副本，页面都可以返回任何缓存版本。这有多危险？

缓存发生在操作之前。您可能需要自定义授权机制来处理缓存场景。

看看我不久前发布的一个问题 -MVC 自定义身份验证、授权和角色实现 https://stackoverflow.com/questions/8567358/mvc-custom-authentication-authorization-and-roles-implementation.

我认为对您有帮助的部分是自定义授权属性OnAuthorize()方法处理缓存。

下面是一个代码块示例：

/// <summary>
/// Uses injected authorization service to determine if the session user 
/// has necessary role privileges.
/// </summary>
/// <remarks>As authorization code runs at the action level, after the 
/// caching module, our authorization code is hooked into the caching 
/// mechanics, to ensure unauthorized users are not served up a 
/// prior-authorized page. 
/// Note: Special thanks to TheCloudlessSky on StackOverflow.
/// </remarks>
public void OnAuthorization(AuthorizationContext filterContext)
{
    // User must be authenticated and Session not be null
    if (!filterContext.HttpContext.User.Identity.IsAuthenticated || filterContext.HttpContext.Session == null)
        HandleUnauthorizedRequest(filterContext);
    else {
        // if authorized, handle cache validation
        if (_authorizationService.IsAuthorized((UserSessionInfoViewModel)filterContext.HttpContext.Session["user"], _authorizedRoles)) {
            var cache = filterContext.HttpContext.Response.Cache;
            cache.SetProxyMaxAge(new TimeSpan(0));
            cache.AddValidationCallback((HttpContext context, object o, ref HttpValidationStatus status) => AuthorizeCache(context), null);
        }
        else
            HandleUnauthorizedRequest(filterContext);             
    }
}

/// <summary>
/// Ensures that authorization is checked on cached pages.
/// </summary>
/// <param name="httpContext"></param>
/// <returns></returns>
public HttpValidationStatus AuthorizeCache(HttpContext httpContext)
{
    if (httpContext.Session == null)
        return HttpValidationStatus.Invalid;
    return _authorizationService.IsAuthorized((UserSessionInfoViewModel) httpContext.Session["user"], _authorizedRoles) 
        ? HttpValidationStatus.Valid 
        : HttpValidationStatus.IgnoreThisRequest;
}