Question

我正在使用针对Azure AD的OWIN和OpenID Connect测试webproject。我正在使用此示例中的大部分代码：https://github.com/Azure-Samples/active-directory-dotnet-webapp-webapi-openidconnect

我遇到一个问题，我在这个文件的第27行得到一个空例外：https://github.com/Azure-Samples/active-directory-dotnet-webapp-webapi-openidconnect/blob/master/TodoListWebApp/Utils/NaiveSessionCache.cs

我得到异常，因为HttpContext.Current为null。

我可以看到从BeforeAccessNotification（）调用Load（）。

我的框架版本是4.5.2，我的web.config中有<httpRuntime targetFramework="4.5.2" ... >。

为什么HttpContext.Current在此上下文中为空？

更新：

我与示例的唯一区别是我的控制器上的ActionResult不是异步的。我在一个异步任务中调用AcquireTokenSilentAsync，该异步任务是使用标准ActionResult中的.Wait（）调用的。我在CMS中工作，不允许我使用异步ActionResults。

这是OnAuthorizationCodeReceived：

    private async Task OnAuthorizationCodeReceived(AuthorizationCodeReceivedNotification context)
    {
        var code = context.Code;

        var credential = new ClientCredential(ClientId, AppKey);

        var userObjectID =
            context.AuthenticationTicket.Identity.FindFirst(
                "http://schemas.microsoft.com/identity/claims/objectidentifier").Value;

        var authContext = new AuthenticationContext(Authority, new NaiveSessionCache(userObjectID));

        var uri = new Uri(HttpContext.Current.Request.Url.GetLeftPart(UriPartial.Path));

        var result = await authContext.AcquireTokenByAuthorizationCodeAsync(code, uri, credential, GraphUrl);
    }

这是堆栈跟踪：

[NullReferenceException: Object reference not set to an instance of an object.]
   MyTest.NaiveSessionCache.Load() in C:\Workspace\MyTest\src\Website\NaiveSessionCache.cs:26
   MyTest.NaiveSessionCache.BeforeAccessNotification(TokenCacheNotificationArgs args) in C:\Workspace\MyTest\src\Website\NaiveSessionCache.cs:53
   Microsoft.IdentityModel.Clients.ActiveDirectory.TokenCache.OnBeforeAccess(TokenCacheNotificationArgs args) +94
   Microsoft.IdentityModel.Clients.ActiveDirectory.<RunAsync>d__55.MoveNext() +3751
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +14139120
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +62
   Microsoft.IdentityModel.Clients.ActiveDirectory.<AcquireTokenByAuthorizationCodeCommonAsync>d__48.MoveNext() +479
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +14139120
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +62
   Microsoft.IdentityModel.Clients.ActiveDirectory.<AcquireTokenByAuthorizationCodeAsync>d__30.MoveNext() +386
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +14139120
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +62
   System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() +31
   MyTest.<OnAuthorizationCodeReceived>d__12.MoveNext() in C:\Workspace\MyTest\src\Website\Startup.cs:86
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +14139120
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +62
   System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task) +14139265
   Microsoft.Owin.Security.OpenIdConnect.<AuthenticateCoreAsync>d__1a.MoveNext() +5965
   System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() +31
   Microsoft.Owin.Security.OpenIdConnect.<AuthenticateCoreAsync>d__1a.MoveNext() +7305
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +14139120
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +62
   Microsoft.Owin.Security.Infrastructure.<BaseInitializeAsync>d__0.MoveNext() +824
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +14139120
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +62
   Microsoft.Owin.Security.Infrastructure.<Invoke>d__0.MoveNext() +334
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +14139120
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +62
   Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.<RunApp>d__5.MoveNext() +204
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +14139120
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +62
   Microsoft.Owin.Security.Infrastructure.<Invoke>d__0.MoveNext() +777
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +14139120
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +62
   Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.<RunApp>d__5.MoveNext() +204
   System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +14139120
   System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +62
   Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.<DoFinalWork>d__2.MoveNext() +194
   Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.StageAsyncResult.End(IAsyncResult ar) +96
   System.Web.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +363
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +157

Answer 1

我得到了它的工作。您必须传递HttpContextBase才能创建会话缓存对象。 HttpContext.Current在另一个线程上执行时变为null。

using Microsoft.IdentityModel.Clients.ActiveDirectory;
using System.Threading;
using System.Web;

namespace AzureADWebApp
{
public class NaiveSessionCache: TokenCache
{
    private static ReaderWriterLockSlim SessionLock = new ReaderWriterLockSlim(LockRecursionPolicy.NoRecursion);
    string UserObjectId = string.Empty;
    string CacheId = string.Empty;
    HttpContextBase HttpContext = null;
    public MSALSessionCache(string userId, HttpContextBase httpContext)
    {
        UserObjectId = userId;
        CacheId = UserObjectId + "_TokenCache";
        this.HttpContext = httpContext;
        this.AfterAccess = AfterAccessNotification;
        this.BeforeAccess = BeforeAccessNotification;
        Load();
    }

    public void Load()
    {
        SessionLock.EnterReadLock();
        this.Deserialize((byte[])HttpContext.Session[CacheId]);
        SessionLock.ExitReadLock();
    }

    public void Persist()
    {
        SessionLock.EnterWriteLock();

        // Optimistically set HasStateChanged to false. We need to do it early to avoid losing changes made by a concurrent thread.
        this.HasStateChanged = false;

        // Reflect changes in the persistent store
        HttpContext.Session[CacheId] = this.Serialize();
        SessionLock.ExitWriteLock();
    }

    // Empties the persistent store.
    public override void Clear()
    {
        base.Clear();
        HttpContext.Session.Remove(CacheId);
    }

    // Triggered right before ADAL needs to access the cache.
    // Reload the cache from the persistent store in case it changed since the last access.
    void BeforeAccessNotification(TokenCacheNotificationArgs args)
    {
        Load();
    }

    // Triggered right after ADAL accessed the cache.
    void AfterAccessNotification(TokenCacheNotificationArgs args)
    {
        // if the access operation resulted in a cache update
        if (this.HasStateChanged)
        {
            Persist();
        }
    }
}
}

使用AuthenticationCodeReceived Notification中的附加参数创建您的NaiveSessionCache对象：

 new NaiveSessionCache(userObjectID, notification.OwinContext.Environment["System.Web.HttpContextBase"] as HttpContextBase));

Answer 2

ADAL为从版本3.13.0开始的所有异步方法添加configureAwait（false），这导致NaiveSession中的HttpContext.Current变为NULL，因为它很可能在新线程中。您可以使用3.12.0版本的ADAL，它可以正常工作。

Answer 3

我不确定它是不是你的情况，但有时HttpContext.Current null的根本原因是web.config中缺少键：

<add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" />

Answer 4

通过使用异步调用添加wait，您将启动另一个HTTPContext.Current为null的线程。您需要调整nativesession提供程序以将httpcontext作为参数或更改程序流以使用await运算符在单个线程中使用它，以便您可以适当地访问变量。

TokenCache.BeforeAccess上的HttpContext.Current为null

4 个答案: