Deprecate the IAuthenticationHandler property

src/Microsoft.AspNetCore.Http.Features/Authentication/IHttpAuthenticationFeature.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.Security.Claims;
 
 namespace Microsoft.AspNetCore.Http.Features.Authentication
@@ -9,6 +10,7 @@ public interface IHttpAuthenticationFeature
     {
         ClaimsPrincipal User { get; set; }
 
+        [Obsolete("This is obsolete and will be removed in a future version. See https://go.microsoft.com/fwlink/?linkid=845470.")]
         IAuthenticationHandler Handler { get; set; }
     }
 }

src/Microsoft.AspNetCore.Http/Authentication/DefaultAuthenticationManager.cs

@@ -42,7 +42,9 @@ public virtual void Uninitialize()
 
         public override IEnumerable<AuthenticationDescription> GetAuthenticationSchemes()
         {
+#pragma warning disable CS0618 // Type or member is obsolete
             var handler = HttpAuthenticationFeature.Handler;
+#pragma warning restore CS0618 // Type or member is obsolete
             if (handler == null)
             {
                 return new AuthenticationDescription[0];
@@ -61,7 +63,9 @@ public override async Task AuthenticateAsync(AuthenticateContext context)
                 throw new ArgumentNullException(nameof(context));
             }
 
+#pragma warning disable CS0618 // Type or member is obsolete
             var handler = HttpAuthenticationFeature.Handler;
+#pragma warning restore CS0618 // Type or member is obsolete
             if (handler != null)
             {
                 await handler.AuthenticateAsync(context);
@@ -80,7 +84,9 @@ public override async Task<AuthenticateInfo> GetAuthenticateInfoAsync(string aut
                 throw new ArgumentNullException(nameof(authenticationScheme));
             }
 
+#pragma warning disable CS0618 // Type or member is obsolete
             var handler = HttpAuthenticationFeature.Handler;
+#pragma warning restore CS0618 // Type or member is obsolete
             var context = new AuthenticateContext(authenticationScheme);
             if (handler != null)
             {
@@ -107,7 +113,9 @@ public override async Task ChallengeAsync(string authenticationScheme, Authentic
                 throw new ArgumentException(nameof(authenticationScheme));
             }
 
+#pragma warning disable CS0618 // Type or member is obsolete
             var handler = HttpAuthenticationFeature.Handler;
+#pragma warning restore CS0618 // Type or member is obsolete
 
             var challengeContext = new ChallengeContext(authenticationScheme, properties?.Items, behavior);
             if (handler != null)
@@ -133,7 +141,9 @@ public override async Task SignInAsync(string authenticationScheme, ClaimsPrinci
                 throw new ArgumentNullException(nameof(principal));
             }
 
+#pragma warning disable CS0618 // Type or member is obsolete
             var handler = HttpAuthenticationFeature.Handler;
+#pragma warning restore CS0618 // Type or member is obsolete
 
             var signInContext = new SignInContext(authenticationScheme, principal, properties?.Items);
             if (handler != null)
@@ -154,7 +164,9 @@ public override async Task SignOutAsync(string authenticationScheme, Authenticat
                 throw new ArgumentException(nameof(authenticationScheme));
             }
 
+#pragma warning disable CS0618 // Type or member is obsolete
             var handler = HttpAuthenticationFeature.Handler;
+#pragma warning restore CS0618 // Type or member is obsolete
 
             var signOutContext = new SignOutContext(authenticationScheme, properties?.Items);
             if (handler != null)