add support for context.SetSessionStateBehavior

src/Microsoft.AspNetCore.SystemWebAdapters.CoreServices/SessionMiddleware.cs

@@ -31,9 +31,33 @@ public SessionMiddleware(RequestDelegate next, ILogger<SessionMiddleware> logger
     }
 
     public Task InvokeAsync(HttpContextCore context)
-        => context.GetEndpoint()?.Metadata.GetMetadata<SessionAttribute>() is { Behavior: not SessionBehavior.None } metadata
+    {
+        var feature = context.Features.Get<ISessionStateFeature>();
+        var metadata = context.GetEndpoint()?.Metadata.GetMetadata<SessionAttribute>();
+
+        if (feature != null && feature.State != SessionStateBehavior.Default)
+        {
+            // override metadata
+            metadata = metadata ?? new SessionAttribute();
+            switch (feature.State)
+            {
+                case SessionStateBehavior.Disabled:
+                    metadata.Behavior = SessionBehavior.None;
+                    break;
+                case SessionStateBehavior.ReadOnly:
+                    metadata.IsReadOnly = true;
+                    break;
+                case SessionStateBehavior.Required:
+                    metadata.Behavior = SessionBehavior.Preload;
+                    break;
+            }
+        }
+
+        return metadata is { Behavior: not SessionBehavior.None }
             ? ManageStateAsync(context, metadata)
             : _next(context);
+    }
+
 
     private async Task ManageStateAsync(HttpContextCore context, SessionAttribute metadata)
     {

src/Microsoft.AspNetCore.SystemWebAdapters/Adapters/SessionState/ISessionStateFeature.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#if NETCOREAPP
+using System.Web.SessionState;
+
+namespace Microsoft.AspNetCore.SystemWebAdapters.SessionState;
+
+internal interface ISessionStateFeature
+{
+    SessionStateBehavior State { get; set; }
+}
+#endif

src/Microsoft.AspNetCore.SystemWebAdapters/Generated/Ref.Standard.cs

@@ -157,6 +157,7 @@ internal HttpContext() { }
         public void RewritePath(string path, bool rebaseClientPath) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         public void RewritePath(string filePath, string pathInfo, string queryString) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         public void RewritePath(string filePath, string pathInfo, string queryString, bool setClientFilePath) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public void SetSessionStateBehavior(System.Web.SessionState.SessionStateBehavior sessionStateBehavior) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         object System.IServiceProvider.GetService(System.Type service) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
     }
     public partial class HttpContextBase : System.IServiceProvider
@@ -184,6 +185,7 @@ public partial class HttpContextBase : System.IServiceProvider
         public virtual void RewritePath(string path, bool rebaseClientPath) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         public virtual void RewritePath(string filePath, string pathInfo, string queryString) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         public virtual void RewritePath(string filePath, string pathInfo, string queryString, bool setClientFilePath) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public virtual void SetSessionStateBehavior(System.Web.SessionState.SessionStateBehavior sessionStateBehavior) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
     }
     public partial class HttpContextWrapper : System.Web.HttpContextBase
     {
@@ -209,6 +211,7 @@ public partial class HttpContextWrapper : System.Web.HttpContextBase
         public override void RewritePath(string path, bool rebaseClientPath) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         public override void RewritePath(string filePath, string pathInfo, string queryString) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         public override void RewritePath(string filePath, string pathInfo, string queryString, bool setClientFilePath) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public override void SetSessionStateBehavior(System.Web.SessionState.SessionStateBehavior sessionStateBehavior) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
     }
     public sealed partial class HttpCookie
     {
@@ -817,6 +820,13 @@ internal HttpSessionState() { }
         public void Remove(string name) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         public void RemoveAll() { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
     }
+    public enum SessionStateBehavior
+    {
+        Default = 0,
+        Disabled = 3,
+        ReadOnly = 2,
+        Required = 1,
+    }
     public enum SessionStateMode
     {
         Custom = 4,

src/Microsoft.AspNetCore.SystemWebAdapters/Generated/TypeForwards.Framework.cs

@@ -68,4 +68,5 @@
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.Configuration.HttpCapabilitiesBase))]
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.Hosting.HostingEnvironment))]
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.SessionState.HttpSessionState))]
+[assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.SessionState.SessionStateBehavior))]
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Web.SessionState.SessionStateMode))]

src/Microsoft.AspNetCore.SystemWebAdapters/HttpContext.cs

@@ -11,6 +11,8 @@
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Features.Authentication;
 using Microsoft.AspNetCore.SystemWebAdapters;
+using Microsoft.AspNetCore.SystemWebAdapters.Internal;
+using Microsoft.AspNetCore.SystemWebAdapters.SessionState;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 
@@ -151,6 +153,18 @@ public ISubscriptionToken DisposeOnPipelineCompleted(IDisposable target)
         _context.Response.RegisterForDispose(token);
         return token;
     }
+    public void SetSessionStateBehavior(SessionStateBehavior sessionStateBehavior)
+    {
+        if (_context.Features.Get<ISessionStateFeature>() is { } feature)
+        {
+            feature.State = sessionStateBehavior;
+        }
+        else
+        {
+            var newFeature = new SessionStateFeature() { State = sessionStateBehavior };
+            _context.Features.Set<ISessionStateFeature>(newFeature);
+        }
+    }
 
     [return: NotNullIfNotNull(nameof(context))]
     public static implicit operator HttpContext?(HttpContextCore? context) => context?.GetAdapter();

src/Microsoft.AspNetCore.SystemWebAdapters/HttpContextBase.cs

@@ -4,6 +4,7 @@
 using System.Collections;
 using System.Security.Principal;
 using System.Diagnostics.CodeAnalysis;
+using System.Web.SessionState;
 using Microsoft.AspNetCore.SystemWebAdapters;
 
 namespace System.Web
@@ -67,5 +68,7 @@ public virtual IPrincipal User
         public virtual void RewritePath(string filePath, string pathInfo, string? queryString) => throw new NotImplementedException();
 
         public virtual void RewritePath(string filePath, string pathInfo, string? queryString, bool setClientFilePath) => throw new NotImplementedException();
+
+        public virtual void SetSessionStateBehavior(SessionStateBehavior sessionStateBehavior) => throw new NotImplementedException();
     }
 }

src/Microsoft.AspNetCore.SystemWebAdapters/HttpContextWrapper.cs

@@ -79,5 +79,7 @@ public override IPrincipal User
         public override void RewritePath(string filePath, string pathInfo, string? queryString) => _context.RewritePath(filePath, pathInfo, queryString);
 
         public override void RewritePath(string filePath, string pathInfo, string? queryString, bool setClientFilePath) => _context.RewritePath(filePath, pathInfo, queryString, setClientFilePath);
+
+        public override void SetSessionStateBehavior(SessionStateBehavior sessionStateBehavior) => _context.SetSessionStateBehavior(sessionStateBehavior);
     }
 }

src/Microsoft.AspNetCore.SystemWebAdapters/Internal/SessionStateFeature.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Web.SessionState;
+using Microsoft.AspNetCore.SystemWebAdapters.SessionState;
+
+namespace Microsoft.AspNetCore.SystemWebAdapters.Internal
+{
+    internal class SessionStateFeature: ISessionStateFeature
+    {
+        public SessionStateBehavior State { get; set; }
+    }
+}

src/Microsoft.AspNetCore.SystemWebAdapters/SessionState/SessionStateBehavior.cs

@@ -0,0 +1,12 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Web.SessionState;
+
+public enum SessionStateBehavior
+{
+    Default = 0,
+    Required = 1,
+    ReadOnly = 2,
+    Disabled = 3
+};